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 $198.46   13.431%   $225.1152   $225.12   $225.10   $225.10  
  Purchase #2 $240.86   11.620%   $268.8479   $268.85   $268.85   $268.80  
  Purchase #3 $237.29   11.248%   $263.9804   $263.98   $264.00   $264.00  
  Purchase #4 $82.34   11.147%   $91.5184   $91.52   $91.50   $91.50  
  Purchase #5 $46.93   3.755%   $48.6922   $48.69   $48.70   $48.70  
  Purchase #6 $16.33   6.693%   $17.423   $17.42   $17.40   $17.40  
  Purchase #7 $132.42   4.600%   $138.5113   $138.51   $138.50   $138.50  
  7 purchase totals = $954.63       $1,054.0884   $1,054.09   $1,054.05   $1,054.00