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 $62.89   9.195%   $68.6727   $68.67   $68.65   $68.70  
  Purchase #2 $22.56   10.129%   $24.8451   $24.85   $24.85   $24.80  
  Purchase #3 $195.64   4.557%   $204.5553   $204.56   $204.55   $204.60  
  Purchase #4 $72.46   11.739%   $80.9661   $80.97   $80.95   $81.00  
  Purchase #5 $100.31   7.669%   $108.0028   $108.00   $108.00   $108.00  
  Purchase #6 $193.48   8.813%   $210.5314   $210.53   $210.55   $210.50  
  Purchase #7 $155.54   9.302%   $170.0083   $170.01   $170.00   $170.00  
  7 purchase totals = $802.88       $867.5817   $867.59   $867.55   $867.60