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 $168.95   4.646%   $176.7994   $176.80   $176.80   $176.80  
  Purchase #2 $53.56   13.859%   $60.9829   $60.98   $61.00   $61.00  
  Purchase #3 $7.59   4.790%   $7.9536   $7.95   $7.95   $8.00  
  Purchase #4 $208.48   8.457%   $226.1112   $226.11   $226.10   $226.10  
  Purchase #5 $54.81   10.189%   $60.3946   $60.39   $60.40   $60.40  
  Purchase #6 $232.29   7.417%   $249.5189   $249.52   $249.50   $249.50  
  Purchase #7 $83.72   9.600%   $91.7571   $91.76   $91.75   $91.80  
  7 purchase totals = $809.40       $873.5177   $873.51   $873.50   $873.60