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 $166.55   12.850%   $187.9517   $187.95   $187.95   $188.00  
  Purchase #2 $189.43   5.235%   $199.3467   $199.35   $199.35   $199.30  
  Purchase #3 $198.76   6.799%   $212.2737   $212.27   $212.25   $212.30  
  Purchase #4 $231.26   6.783%   $246.9464   $246.95   $246.95   $246.90  
  Purchase #5 $88.56   7.770%   $95.4411   $95.44   $95.45   $95.40  
  Purchase #6 $133.69   5.822%   $141.4734   $141.47   $141.45   $141.50  
  Purchase #7 $137.46   10.235%   $151.529   $151.53   $151.55   $151.50  
  7 purchase totals = $1,145.71       $1,234.9620   $1,234.96   $1,234.95   $1,234.90