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 $44.93   5.138%   $47.2385   $47.24   $47.25   $47.20  
  Purchase #2 $244.38   6.445%   $260.1303   $260.13   $260.15   $260.10  
  Purchase #3 $249.88   13.575%   $283.8012   $283.80   $283.80   $283.80  
  Purchase #4 $73.84   8.216%   $79.9067   $79.91   $79.90   $79.90  
  Purchase #5 $11.59   9.791%   $12.7248   $12.72   $12.70   $12.70  
  Purchase #6 $61.34   7.328%   $65.835   $65.84   $65.85   $65.80  
  Purchase #7 $241.95   13.234%   $273.9697   $273.97   $273.95   $274.00  
  7 purchase totals = $927.91       $1,023.6062   $1,023.61   $1,023.60   $1,023.50