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 $226.34   12.143%   $253.8245   $253.82   $253.80   $253.80  
  Purchase #2 $211.53   3.691%   $219.3376   $219.34   $219.35   $219.30  
  Purchase #3 $194.30   11.434%   $216.5163   $216.52   $216.50   $216.50  
  Purchase #4 $92.64   11.410%   $103.2102   $103.21   $103.20   $103.20  
  Purchase #5 $165.28   5.733%   $174.7555   $174.76   $174.75   $174.80  
  Purchase #6 $186.72   13.646%   $212.1998   $212.20   $212.20   $212.20  
  Purchase #7 $244.63   3.487%   $253.1602   $253.16   $253.15   $253.20  
  7 purchase totals = $1,321.44       $1,433.0041   $1,433.01   $1,432.95   $1,433.00