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 $244.79   11.843%   $273.7805   $273.78   $273.80   $273.80  
  Purchase #2 $53.35   4.415%   $55.7054   $55.71   $55.70   $55.70  
  Purchase #3 $157.89   12.205%   $177.1605   $177.16   $177.15   $177.20  
  Purchase #4 $152.72   10.649%   $168.9832   $168.98   $169.00   $169.00  
  Purchase #5 $50.78   9.604%   $55.6569   $55.66   $55.65   $55.70  
  Purchase #6 $121.56   7.266%   $130.3925   $130.39   $130.40   $130.40  
  Purchase #7 $185.99   4.300%   $193.9876   $193.99   $194.00   $194.00  
  7 purchase totals = $967.08       $1,055.6666   $1,055.67   $1,055.70   $1,055.80