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 $53.63   5.401%   $56.5266   $56.53   $56.55   $56.50  
  Purchase #2 $8.93   9.694%   $9.7957   $9.80   $9.80   $9.80  
  Purchase #3 $236.89   4.504%   $247.5595   $247.56   $247.55   $247.60  
  Purchase #4 $213.55   10.675%   $236.3465   $236.35   $236.35   $236.30  
  Purchase #5 $232.52   5.169%   $244.539   $244.54   $244.55   $244.50  
  Purchase #6 $156.99   7.322%   $168.4848   $168.48   $168.50   $168.50  
  Purchase #7 $39.25   5.208%   $41.2941   $41.29   $41.30   $41.30  
  7 purchase totals = $941.76       $1,004.5462   $1,004.55   $1,004.60   $1,004.50