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 $67.46   4.208%   $70.2987   $70.30   $70.30   $70.30  
  Purchase #2 $126.74   11.847%   $141.7549   $141.75   $141.75   $141.80  
  Purchase #3 $27.64   11.670%   $30.8656   $30.87   $30.85   $30.90  
  Purchase #4 $228.34   13.676%   $259.5678   $259.57   $259.55   $259.60  
  Purchase #5 $161.30   7.595%   $173.5507   $173.55   $173.55   $173.60  
  Purchase #6 $124.82   12.255%   $140.1167   $140.12   $140.10   $140.10  
  Purchase #7 $131.79   13.171%   $149.1481   $149.15   $149.15   $149.10  
  7 purchase totals = $868.09       $965.3025   $965.31   $965.25   $965.40