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 $48.65   6.608%   $51.8648   $51.86   $51.85   $51.90  
  Purchase #2 $26.39   4.577%   $27.5979   $27.60   $27.60   $27.60  
  Purchase #3 $87.55   8.198%   $94.7273   $94.73   $94.75   $94.70  
  Purchase #4 $179.58   10.464%   $198.3713   $198.37   $198.35   $198.40  
  Purchase #5 $82.39   10.831%   $91.3137   $91.31   $91.30   $91.30  
  Purchase #6 $8.78   5.593%   $9.2711   $9.27   $9.25   $9.30  
  Purchase #7 $53.60   12.573%   $60.3391   $60.34   $60.35   $60.30  
  7 purchase totals = $486.94       $533.4852   $533.48   $533.45   $533.50