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 $11.29   6.372%   $12.0094   $12.01   $12.00   $12.00  
  Purchase #2 $53.42   3.363%   $55.2165   $55.22   $55.20   $55.20  
  Purchase #3 $132.84   3.842%   $137.9437   $137.94   $137.95   $137.90  
  Purchase #4 $38.99   13.256%   $44.1585   $44.16   $44.15   $44.20  
  Purchase #5 $236.77   8.863%   $257.7549   $257.75   $257.75   $257.80  
  Purchase #6 $179.27   8.507%   $194.5205   $194.52   $194.50   $194.50  
  Purchase #7 $231.93   3.277%   $239.5303   $239.53   $239.55   $239.50  
  7 purchase totals = $884.51       $941.1338   $941.13   $941.10   $941.10