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 $225.47   8.796%   $245.3023   $245.30   $245.30   $245.30  
  Purchase #2 $156.61   12.788%   $176.6373   $176.64   $176.65   $176.60  
  Purchase #3 $209.93   12.602%   $236.3854   $236.39   $236.40   $236.40  
  Purchase #4 $19.86   5.874%   $21.0266   $21.03   $21.05   $21.00  
  Purchase #5 $93.98   10.578%   $103.9212   $103.92   $103.90   $103.90  
  Purchase #6 $161.48   7.668%   $173.8623   $173.86   $173.85   $173.90  
  Purchase #7 $220.85   6.609%   $235.446   $235.45   $235.45   $235.40  
  7 purchase totals = $1,088.18       $1,192.5811   $1,192.59   $1,192.60   $1,192.50