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 $215.27   3.598%   $223.0154   $223.02   $223.00   $223.00  
  Purchase #2 $118.31   13.473%   $134.2499   $134.25   $134.25   $134.20  
  Purchase #3 $121.92   8.608%   $132.4149   $132.41   $132.40   $132.40  
  Purchase #4 $148.88   3.439%   $154   $154.00   $154.00   $154.00  
  Purchase #5 $48.36   10.746%   $53.5568   $53.56   $53.55   $53.60  
  Purchase #6 $78.67   13.199%   $89.0537   $89.05   $89.05   $89.10  
  Purchase #7 $14.57   3.218%   $15.0389   $15.04   $15.05   $15.00  
  7 purchase totals = $745.98       $801.3296   $801.33   $801.30   $801.30