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 $71.73   6.859%   $76.65   $76.65   $76.65   $76.70  
  Purchase #2 $240.75   11.232%   $267.791   $267.79   $267.80   $267.80  
  Purchase #3 $241.72   9.562%   $264.8333   $264.83   $264.85   $264.80  
  Purchase #4 $35.52   6.307%   $37.7602   $37.76   $37.75   $37.80  
  Purchase #5 $101.82   13.576%   $115.6431   $115.64   $115.65   $115.60  
  Purchase #6 $153.85   5.227%   $161.8917   $161.89   $161.90   $161.90  
  Purchase #7 $164.54   5.332%   $173.3133   $173.31   $173.30   $173.30  
  7 purchase totals = $1,009.93       $1,097.8826   $1,097.87   $1,097.90   $1,097.90