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 $245.86   8.674%   $267.1859   $267.19   $267.20   $267.20  
  Purchase #2 $227.87   11.789%   $254.7336   $254.73   $254.75   $254.70  
  Purchase #3 $199.29   12.467%   $224.1355   $224.14   $224.15   $224.10  
  Purchase #4 $60.41   13.515%   $68.5744   $68.57   $68.55   $68.60  
  Purchase #5 $211.90   3.822%   $219.9988   $220.00   $220.00   $220.00  
  Purchase #6 $108.88   3.829%   $113.049   $113.05   $113.05   $113.00  
  Purchase #7 $230.61   11.291%   $256.6482   $256.65   $256.65   $256.60  
  7 purchase totals = $1,284.82       $1,404.3254   $1,404.33   $1,404.35   $1,404.20