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 $48.75   8.621%   $52.9527   $52.95   $52.95   $53.00  
  Purchase #2 $159.86   9.694%   $175.3568   $175.36   $175.35   $175.40  
  Purchase #3 $64.33   5.534%   $67.89   $67.89   $67.90   $67.90  
  Purchase #4 $33.97   9.609%   $37.2342   $37.23   $37.25   $37.20  
  Purchase #5 $139.76   9.620%   $153.2049   $153.20   $153.20   $153.20  
  Purchase #6 $204.56   8.339%   $221.6183   $221.62   $221.60   $221.60  
  Purchase #7 $59.78   7.161%   $64.0608   $64.06   $64.05   $64.10  
  7 purchase totals = $711.01       $772.3177   $772.31   $772.30   $772.40