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 $125.26   10.789%   $138.7743   $138.77   $138.75   $138.80  
  Purchase #2 $85.41   11.175%   $94.9546   $94.95   $94.95   $95.00  
  Purchase #3 $117.93   9.458%   $129.0838   $129.08   $129.10   $129.10  
  Purchase #4 $163.84   8.226%   $177.3175   $177.32   $177.30   $177.30  
  Purchase #5 $32.85   5.746%   $34.7376   $34.74   $34.75   $34.70  
  Purchase #6 $149.57   13.580%   $169.8816   $169.88   $169.90   $169.90  
  Purchase #7 $226.57   10.754%   $250.9353   $250.94   $250.95   $250.90  
  7 purchase totals = $901.43       $995.6847   $995.68   $995.70   $995.70