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 $237.34   13.306%   $268.9205   $268.92   $268.90   $268.90  
  Purchase #2 $63.77   6.594%   $67.975   $67.98   $68.00   $68.00  
  Purchase #3 $35.27   5.570%   $37.2345   $37.23   $37.25   $37.20  
  Purchase #4 $51.56   13.454%   $58.4969   $58.50   $58.50   $58.50  
  Purchase #5 $219.93   8.570%   $238.778   $238.78   $238.80   $238.80  
  Purchase #6 $176.72   4.154%   $184.0609   $184.06   $184.05   $184.10  
  Purchase #7 $236.77   13.399%   $268.4948   $268.49   $268.50   $268.50  
  7 purchase totals = $1,021.36       $1,123.9606   $1,123.96   $1,124.00   $1,124.00