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 $35.29   6.755%   $37.6738   $37.67   $37.65   $37.70  
  Purchase #2 $234.59   13.665%   $266.6467   $266.65   $266.65   $266.60  
  Purchase #3 $44.88   11.195%   $49.9043   $49.90   $49.90   $49.90  
  Purchase #4 $83.87   11.395%   $93.427   $93.43   $93.45   $93.40  
  Purchase #5 $159.26   7.630%   $171.4115   $171.41   $171.40   $171.40  
  Purchase #6 $59.65   11.472%   $66.493   $66.49   $66.50   $66.50  
  Purchase #7 $120.45   9.295%   $131.6458   $131.65   $131.65   $131.60  
  7 purchase totals = $737.99       $817.2021   $817.20   $817.20   $817.10