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 $117.90   6.141%   $125.1402   $125.14   $125.15   $125.10  
  Purchase #2 $240.56   5.268%   $253.2327   $253.23   $253.25   $253.20  
  Purchase #3 $183.45   10.694%   $203.0681   $203.07   $203.05   $203.10  
  Purchase #4 $24.78   11.171%   $27.5482   $27.55   $27.55   $27.50  
  Purchase #5 $68.30   5.292%   $71.9144   $71.91   $71.90   $71.90  
  Purchase #6 $77.88   13.350%   $88.277   $88.28   $88.30   $88.30  
  Purchase #7 $194.66   3.841%   $202.1369   $202.14   $202.15   $202.10  
  7 purchase totals = $907.53       $971.3175   $971.32   $971.35   $971.20