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 $205.48   10.429%   $226.9095   $226.91   $226.90   $226.90  
  Purchase #2 $214.55   7.561%   $230.7721   $230.77   $230.75   $230.80  
  Purchase #3 $159.26   11.816%   $178.0782   $178.08   $178.10   $178.10  
  Purchase #4 $118.56   3.238%   $122.399   $122.40   $122.40   $122.40  
  Purchase #5 $227.88   5.630%   $240.7096   $240.71   $240.70   $240.70  
  Purchase #6 $205.97   12.831%   $232.398   $232.40   $232.40   $232.40  
  Purchase #7 $234.66   12.334%   $263.603   $263.60   $263.60   $263.60  
  7 purchase totals = $1,366.36       $1,494.8694   $1,494.87   $1,494.85   $1,494.90