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 $69.92   5.801%   $73.9761   $73.98   $74.00   $74.00  
  Purchase #2 $93.88   3.241%   $96.9227   $96.92   $96.90   $96.90  
  Purchase #3 $71.31   6.391%   $75.8674   $75.87   $75.85   $75.90  
  Purchase #4 $59.90   12.308%   $67.2725   $67.27   $67.25   $67.30  
  Purchase #5 $204.55   8.846%   $222.6445   $222.64   $222.65   $222.60  
  Purchase #6 $197.71   13.856%   $225.1047   $225.10   $225.10   $225.10  
  Purchase #7 $74.67   12.216%   $83.7917   $83.79   $83.80   $83.80  
  7 purchase totals = $771.94       $845.5796   $845.57   $845.55   $845.60