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 $65.53   12.512%   $73.7291   $73.73   $73.75   $73.70  
  Purchase #2 $195.52   5.158%   $205.6049   $205.60   $205.60   $205.60  
  Purchase #3 $84.92   3.867%   $88.2039   $88.20   $88.20   $88.20  
  Purchase #4 $235.89   3.208%   $243.4574   $243.46   $243.45   $243.50  
  Purchase #5 $124.96   10.691%   $138.3195   $138.32   $138.30   $138.30  
  Purchase #6 $183.82   13.359%   $208.3765   $208.38   $208.40   $208.40  
  Purchase #7 $218.95   10.628%   $242.22   $242.22   $242.20   $242.20  
  7 purchase totals = $1,109.59       $1,199.9113   $1,199.91   $1,199.90   $1,199.90