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 $125.87   6.357%   $133.8716   $133.87   $133.85   $133.90  
  Purchase #2 $211.46   7.274%   $226.8416   $226.84   $226.85   $226.80  
  Purchase #3 $177.94   12.350%   $199.9156   $199.92   $199.90   $199.90  
  Purchase #4 $41.53   12.350%   $46.659   $46.66   $46.65   $46.70  
  Purchase #5 $56.57   4.707%   $59.2327   $59.23   $59.25   $59.20  
  Purchase #6 $201.93   12.131%   $226.4261   $226.43   $226.45   $226.40  
  Purchase #7 $80.25   5.720%   $84.8403   $84.84   $84.85   $84.80  
  7 purchase totals = $895.55       $977.7869   $977.79   $977.80   $977.70