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 $220.74   9.751%   $242.2644   $242.26   $242.25   $242.30  
  Purchase #2 $163.48   9.642%   $179.2427   $179.24   $179.25   $179.20  
  Purchase #3 $211.99   10.606%   $234.4737   $234.47   $234.45   $234.50  
  Purchase #4 $66.45   9.790%   $72.9555   $72.96   $72.95   $73.00  
  Purchase #5 $180.68   4.210%   $188.2866   $188.29   $188.30   $188.30  
  Purchase #6 $82.43   10.525%   $91.1058   $91.11   $91.10   $91.10  
  Purchase #7 $92.87   3.244%   $95.8827   $95.88   $95.90   $95.90  
  7 purchase totals = $1,018.64       $1,104.2114   $1,104.21   $1,104.20   $1,104.30