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 $224.35   13.187%   $253.935   $253.94   $253.95   $253.90  
  Purchase #2 $208.31   11.218%   $231.6782   $231.68   $231.70   $231.70  
  Purchase #3 $12.32   13.750%   $14.014   $14.01   $14.00   $14.00  
  Purchase #4 $50.87   5.863%   $53.8525   $53.85   $53.85   $53.90  
  Purchase #5 $167.44   12.413%   $188.2243   $188.22   $188.20   $188.20  
  Purchase #6 $124.32   9.327%   $135.9153   $135.92   $135.90   $135.90  
  Purchase #7 $180.79   12.617%   $203.6003   $203.60   $203.60   $203.60  
  7 purchase totals = $968.40       $1,081.2196   $1,081.22   $1,081.20   $1,081.20