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 $69.79   3.114%   $71.9633   $71.96   $71.95   $72.00  
  Purchase #2 $32.76   3.714%   $33.9767   $33.98   $34.00   $34.00  
  Purchase #3 $246.79   11.205%   $274.4428   $274.44   $274.45   $274.40  
  Purchase #4 $150.48   4.263%   $156.895   $156.90   $156.90   $156.90  
  Purchase #5 $25.54   9.195%   $27.8884   $27.89   $27.90   $27.90  
  Purchase #6 $59.36   3.413%   $61.386   $61.39   $61.40   $61.40  
  Purchase #7 $199.79   8.717%   $217.2057   $217.21   $217.20   $217.20  
  7 purchase totals = $784.51       $843.7579   $843.77   $843.80   $843.80