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 $241.27   11.727%   $269.5637   $269.56   $269.55   $269.60  
  Purchase #2 $33.98   8.323%   $36.8082   $36.81   $36.80   $36.80  
  Purchase #3 $126.85   6.864%   $135.557   $135.56   $135.55   $135.60  
  Purchase #4 $139.98   13.140%   $158.3734   $158.37   $158.35   $158.40  
  Purchase #5 $42.83   11.688%   $47.836   $47.84   $47.85   $47.80  
  Purchase #6 $55.66   6.603%   $59.3352   $59.34   $59.35   $59.30  
  Purchase #7 $216.57   4.496%   $226.307   $226.31   $226.30   $226.30  
  7 purchase totals = $857.14       $933.7805   $933.79   $933.75   $933.80