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 $11.57   6.455%   $12.3168   $12.32   $12.30   $12.30  
  Purchase #2 $244.44   8.420%   $265.0218   $265.02   $265.00   $265.00  
  Purchase #3 $21.40   13.485%   $24.2858   $24.29   $24.30   $24.30  
  Purchase #4 $188.31   9.695%   $206.5667   $206.57   $206.55   $206.60  
  Purchase #5 $52.27   12.420%   $58.7619   $58.76   $58.75   $58.80  
  Purchase #6 $243.52   4.107%   $253.5214   $253.52   $253.50   $253.50  
  Purchase #7 $235.53   3.170%   $242.9963   $243.00   $243.00   $243.00  
  7 purchase totals = $997.04       $1,063.4707   $1,063.48   $1,063.40   $1,063.50