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 $49.98   11.669%   $55.8122   $55.81   $55.80   $55.80  
  Purchase #2 $90.77   3.573%   $94.0132   $94.01   $94.00   $94.00  
  Purchase #3 $108.93   5.663%   $115.0987   $115.10   $115.10   $115.10  
  Purchase #4 $246.70   5.573%   $260.4486   $260.45   $260.45   $260.40  
  Purchase #5 $55.39   4.642%   $57.9612   $57.96   $57.95   $58.00  
  Purchase #6 $202.38   8.166%   $218.9064   $218.91   $218.90   $218.90  
  Purchase #7 $53.81   9.119%   $58.7169   $58.72   $58.70   $58.70  
  7 purchase totals = $807.96       $860.9572   $860.96   $860.90   $860.90