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 $217.96   6.752%   $232.6767   $232.68   $232.70   $232.70  
  Purchase #2 $70.36   6.345%   $74.8243   $74.82   $74.80   $74.80  
  Purchase #3 $15.88   9.546%   $17.3959   $17.40   $17.40   $17.40  
  Purchase #4 $231.79   5.109%   $243.6322   $243.63   $243.65   $243.60  
  Purchase #5 $50.32   8.116%   $54.404   $54.40   $54.40   $54.40  
  Purchase #6 $24.69   3.381%   $25.5248   $25.52   $25.50   $25.50  
  Purchase #7 $80.37   4.644%   $84.1024   $84.10   $84.10   $84.10  
  7 purchase totals = $691.37       $732.5603   $732.55   $732.55   $732.50