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 $44.60   6.167%   $47.3505   $47.35   $47.35   $47.40  
  Purchase #2 $84.59   10.425%   $93.4085   $93.41   $93.40   $93.40  
  Purchase #3 $13.43   10.130%   $14.7905   $14.79   $14.80   $14.80  
  Purchase #4 $182.69   3.541%   $189.1591   $189.16   $189.15   $189.20  
  Purchase #5 $182.82   6.343%   $194.4163   $194.42   $194.40   $194.40  
  Purchase #6 $224.75   13.403%   $254.8732   $254.87   $254.85   $254.90  
  Purchase #7 $241.70   9.791%   $265.3648   $265.36   $265.35   $265.40  
  7 purchase totals = $974.58       $1,059.3629   $1,059.36   $1,059.30   $1,059.50