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 $177.98   9.748%   $195.3295   $195.33   $195.35   $195.30  
  Purchase #2 $169.68   4.807%   $177.8365   $177.84   $177.85   $177.80  
  Purchase #3 $186.44   10.146%   $205.3562   $205.36   $205.35   $205.40  
  Purchase #4 $13.66   5.761%   $14.447   $14.45   $14.45   $14.40  
  Purchase #5 $167.57   9.164%   $182.9261   $182.93   $182.95   $182.90  
  Purchase #6 $193.78   6.231%   $205.8544   $205.85   $205.85   $205.90  
  Purchase #7 $244.99   9.400%   $268.0191   $268.02   $268.00   $268.00  
  7 purchase totals = $1,154.10       $1,249.7688   $1,249.78   $1,249.80   $1,249.70