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 $55.89   11.267%   $62.1871   $62.19   $62.20   $62.20  
  Purchase #2 $144.39   10.849%   $160.0549   $160.05   $160.05   $160.10  
  Purchase #3 $143.88   3.182%   $148.4583   $148.46   $148.45   $148.50  
  Purchase #4 $195.27   3.818%   $202.7254   $202.73   $202.75   $202.70  
  Purchase #5 $243.96   8.118%   $263.7647   $263.76   $263.75   $263.80  
  Purchase #6 $161.96   12.301%   $181.8827   $181.88   $181.90   $181.90  
  Purchase #7 $221.97   6.320%   $235.9985   $236.00   $236.00   $236.00  
  7 purchase totals = $1,167.32       $1,255.0716   $1,255.07   $1,255.10   $1,255.20