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 $183.86   6.413%   $195.6509   $195.65   $195.65   $195.70  
  Purchase #2 $69.51   8.652%   $75.524   $75.52   $75.50   $75.50  
  Purchase #3 $38.73   5.201%   $40.7443   $40.74   $40.75   $40.70  
  Purchase #4 $155.29   13.867%   $176.8241   $176.82   $176.80   $176.80  
  Purchase #5 $98.53   9.417%   $107.8086   $107.81   $107.80   $107.80  
  Purchase #6 $123.28   10.707%   $136.4796   $136.48   $136.50   $136.50  
  Purchase #7 $226.29   6.474%   $240.94   $240.94   $240.95   $240.90  
  7 purchase totals = $895.49       $973.9715   $973.96   $973.95   $973.90