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 $213.97   10.747%   $236.9654   $236.97   $236.95   $237.00  
  Purchase #2 $151.40   11.863%   $169.3606   $169.36   $169.35   $169.40  
  Purchase #3 $235.57   9.413%   $257.7442   $257.74   $257.75   $257.70  
  Purchase #4 $233.81   13.698%   $265.8373   $265.84   $265.85   $265.80  
  Purchase #5 $130.26   10.343%   $143.7328   $143.73   $143.75   $143.70  
  Purchase #6 $22.65   10.148%   $24.9485   $24.95   $24.95   $24.90  
  Purchase #7 $58.72   12.232%   $65.9026   $65.90   $65.90   $65.90  
  7 purchase totals = $1,046.38       $1,164.4914   $1,164.49   $1,164.50   $1,164.40