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 $120.86   4.614%   $126.4365   $126.44   $126.45   $126.40  
  Purchase #2 $161.38   9.373%   $176.5061   $176.51   $176.50   $176.50  
  Purchase #3 $146.49   4.416%   $152.959   $152.96   $152.95   $153.00  
  Purchase #4 $62.63   3.765%   $64.988   $64.99   $65.00   $65.00  
  Purchase #5 $131.68   8.594%   $142.9966   $143.00   $143.00   $143.00  
  Purchase #6 $88.76   11.815%   $99.247   $99.25   $99.25   $99.20  
  Purchase #7 $243.56   4.845%   $255.3605   $255.36   $255.35   $255.40  
  7 purchase totals = $955.36       $1,018.4937   $1,018.51   $1,018.50   $1,018.50