Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.35   11.874%   $238.6832   $238.68   $238.70   $238.70  
  Purchase #2 $164.30   10.506%   $181.5614   $181.56   $181.55   $181.60  
  Purchase #3 $246.98   6.468%   $262.9547   $262.95   $262.95   $263.00  
  Purchase #4 $99.54   7.445%   $106.9508   $106.95   $106.95   $107.00  
  Purchase #5 $197.63   11.160%   $219.6855   $219.69   $219.70   $219.70  
  Purchase #6 $211.61   6.858%   $226.1222   $226.12   $226.10   $226.10  
  Purchase #7 $234.61   12.461%   $263.8448   $263.84   $263.85   $263.80  
  7 purchase totals = $1,368.02       $1,499.8026   $1,499.79   $1,499.80   $1,499.90