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 $67.62   8.107%   $73.102   $73.10   $73.10   $73.10  
  Purchase #2 $11.62   13.406%   $13.1778   $13.18   $13.20   $13.20  
  Purchase #3 $209.41   6.808%   $223.6666   $223.67   $223.65   $223.70  
  Purchase #4 $226.33   7.646%   $243.6352   $243.64   $243.65   $243.60  
  Purchase #5 $126.80   3.227%   $130.8918   $130.89   $130.90   $130.90  
  Purchase #6 $26.41   10.246%   $29.116   $29.12   $29.10   $29.10  
  Purchase #7 $194.47   9.787%   $213.5028   $213.50   $213.50   $213.50  
  7 purchase totals = $862.66       $927.0922   $927.10   $927.10   $927.10