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 $119.37   3.843%   $123.9574   $123.96   $123.95   $124.00  
  Purchase #2 $247.35   8.526%   $268.4391   $268.44   $268.45   $268.40  
  Purchase #3 $154.31   9.589%   $169.1068   $169.11   $169.10   $169.10  
  Purchase #4 $62.33   12.137%   $69.895   $69.90   $69.90   $69.90  
  Purchase #5 $218.40   11.289%   $243.0552   $243.06   $243.05   $243.10  
  Purchase #6 $35.29   3.444%   $36.5054   $36.51   $36.50   $36.50  
  Purchase #7 $131.84   11.344%   $146.7959   $146.80   $146.80   $146.80  
  7 purchase totals = $968.89       $1,057.7548   $1,057.78   $1,057.75   $1,057.80