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 $60.58   5.486%   $63.9034   $63.90   $63.90   $63.90  
  Purchase #2 $5.28   12.854%   $5.9587   $5.96   $5.95   $6.00  
  Purchase #3 $155.90   3.127%   $160.775   $160.78   $160.80   $160.80  
  Purchase #4 $80.32   9.384%   $87.8572   $87.86   $87.85   $87.90  
  Purchase #5 $139.84   8.484%   $151.704   $151.70   $151.70   $151.70  
  Purchase #6 $183.67   11.535%   $204.8563   $204.86   $204.85   $204.90  
  Purchase #7 $55.35   13.710%   $62.9385   $62.94   $62.95   $62.90  
  7 purchase totals = $680.94       $737.9931   $738.00   $738.00   $738.10