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 $246.34   7.159%   $263.9755   $263.98   $264.00   $264.00  
  Purchase #2 $5.61   11.251%   $6.2412   $6.24   $6.25   $6.20  
  Purchase #3 $70.73   5.147%   $74.3705   $74.37   $74.35   $74.40  
  Purchase #4 $164.41   4.197%   $171.3103   $171.31   $171.30   $171.30  
  Purchase #5 $178.36   8.701%   $193.8791   $193.88   $193.90   $193.90  
  Purchase #6 $146.34   11.138%   $162.6393   $162.64   $162.65   $162.60  
  Purchase #7 $241.65   4.190%   $251.7751   $251.78   $251.80   $251.80  
  7 purchase totals = $1,053.44       $1,124.1910   $1,124.20   $1,124.25   $1,124.20