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 $60.86   6.289%   $64.6875   $64.69   $64.70   $64.70  
  Purchase #2 $202.57   13.529%   $229.9757   $229.98   $230.00   $230.00  
  Purchase #3 $242.36   11.450%   $270.1102   $270.11   $270.10   $270.10  
  Purchase #4 $29.47   11.183%   $32.7656   $32.77   $32.75   $32.80  
  Purchase #5 $58.54   6.216%   $62.1788   $62.18   $62.20   $62.20  
  Purchase #6 $217.55   8.621%   $236.305   $236.31   $236.30   $236.30  
  Purchase #7 $235.85   4.289%   $245.9656   $245.97   $245.95   $246.00  
  7 purchase totals = $1,047.20       $1,141.9884   $1,142.01   $1,142.00   $1,142.10