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 $48.42   13.468%   $54.9412   $54.94   $54.95   $54.90  
  Purchase #2 $190.36   7.238%   $204.1383   $204.14   $204.15   $204.10  
  Purchase #3 $243.31   10.170%   $268.0546   $268.05   $268.05   $268.10  
  Purchase #4 $23.54   13.232%   $26.6548   $26.65   $26.65   $26.70  
  Purchase #5 $43.26   9.606%   $47.4156   $47.42   $47.40   $47.40  
  Purchase #6 $173.91   11.316%   $193.5897   $193.59   $193.60   $193.60  
  Purchase #7 $36.64   12.582%   $41.25   $41.25   $41.25   $41.30  
  7 purchase totals = $759.44       $836.0442   $836.04   $836.05   $836.10