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 $68.90   6.633%   $73.4701   $73.47   $73.45   $73.50  
  Purchase #2 $100.80   5.347%   $106.1898   $106.19   $106.20   $106.20  
  Purchase #3 $89.48   4.754%   $93.7339   $93.73   $93.75   $93.70  
  Purchase #4 $208.31   6.330%   $221.496   $221.50   $221.50   $221.50  
  Purchase #5 $193.36   8.405%   $209.6119   $209.61   $209.60   $209.60  
  Purchase #6 $245.31   5.282%   $258.2673   $258.27   $258.25   $258.30  
  Purchase #7 $51.80   4.203%   $53.9772   $53.98   $54.00   $54.00  
  7 purchase totals = $957.96       $1,016.7462   $1,016.75   $1,016.75   $1,016.80