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 $56.87   7.292%   $61.017   $61.02   $61.00   $61.00  
  Purchase #2 $104.57   12.799%   $117.9539   $117.95   $117.95   $118.00  
  Purchase #3 $208.36   10.692%   $230.6379   $230.64   $230.65   $230.60  
  Purchase #4 $134.31   13.784%   $152.8233   $152.82   $152.80   $152.80  
  Purchase #5 $29.80   11.682%   $33.2812   $33.28   $33.30   $33.30  
  Purchase #6 $211.75   3.742%   $219.6737   $219.67   $219.65   $219.70  
  Purchase #7 $101.37   4.283%   $105.7117   $105.71   $105.70   $105.70  
  7 purchase totals = $847.03       $921.0987   $921.09   $921.05   $921.10