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 $72.41   3.755%   $75.129   $75.13   $75.15   $75.10  
  Purchase #2 $226.97   11.617%   $253.3371   $253.34   $253.35   $253.30  
  Purchase #3 $232.99   6.314%   $247.701   $247.70   $247.70   $247.70  
  Purchase #4 $228.41   7.142%   $244.723   $244.72   $244.70   $244.70  
  Purchase #5 $177.40   11.236%   $197.3327   $197.33   $197.35   $197.30  
  Purchase #6 $182.47   6.400%   $194.1481   $194.15   $194.15   $194.10  
  Purchase #7 $87.33   5.300%   $91.9585   $91.96   $91.95   $92.00  
  7 purchase totals = $1,207.98       $1,304.3294   $1,304.33   $1,304.35   $1,304.20