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 $191.76   9.279%   $209.5534   $209.55   $209.55   $209.60  
  Purchase #2 $66.87   4.700%   $70.0129   $70.01   $70.00   $70.00  
  Purchase #3 $150.80   10.416%   $166.5073   $166.51   $166.50   $166.50  
  Purchase #4 $220.45   11.729%   $246.3066   $246.31   $246.30   $246.30  
  Purchase #5 $119.74   10.443%   $132.2444   $132.24   $132.25   $132.20  
  Purchase #6 $28.69   11.639%   $32.0292   $32.03   $32.05   $32.00  
  Purchase #7 $86.96   5.648%   $91.8715   $91.87   $91.85   $91.90  
  7 purchase totals = $865.27       $948.5253   $948.52   $948.50   $948.50