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 $186.51   10.590%   $206.2614   $206.26   $206.25   $206.30  
  Purchase #2 $218.27   6.495%   $232.4466   $232.45   $232.45   $232.40  
  Purchase #3 $75.81   10.162%   $83.5138   $83.51   $83.50   $83.50  
  Purchase #4 $125.60   9.532%   $137.5722   $137.57   $137.55   $137.60  
  Purchase #5 $128.52   12.363%   $144.4089   $144.41   $144.40   $144.40  
  Purchase #6 $205.94   5.496%   $217.2585   $217.26   $217.25   $217.30  
  Purchase #7 $42.50   12.630%   $47.8678   $47.87   $47.85   $47.90  
  7 purchase totals = $983.15       $1,069.3292   $1,069.33   $1,069.25   $1,069.40