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 $143.68   11.635%   $160.3972   $160.40   $160.40   $160.40  
  Purchase #2 $223.37   6.686%   $238.3045   $238.30   $238.30   $238.30  
  Purchase #3 $23.43   4.621%   $24.5127   $24.51   $24.50   $24.50  
  Purchase #4 $130.85   12.770%   $147.5595   $147.56   $147.55   $147.60  
  Purchase #5 $158.98   10.237%   $175.2548   $175.25   $175.25   $175.30  
  Purchase #6 $239.35   5.625%   $252.8134   $252.81   $252.80   $252.80  
  Purchase #7 $24.60   11.835%   $27.5114   $27.51   $27.50   $27.50  
  7 purchase totals = $944.26       $1,026.3535   $1,026.34   $1,026.30   $1,026.40