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 $139.95   13.665%   $159.0742   $159.07   $159.05   $159.10  
  Purchase #2 $178.54   10.751%   $197.7348   $197.73   $197.75   $197.70  
  Purchase #3 $136.64   13.162%   $154.6246   $154.62   $154.60   $154.60  
  Purchase #4 $133.73   4.463%   $139.6984   $139.70   $139.70   $139.70  
  Purchase #5 $203.85   11.303%   $226.8912   $226.89   $226.90   $226.90  
  Purchase #6 $60.34   10.250%   $66.5249   $66.52   $66.50   $66.50  
  Purchase #7 $79.76   11.385%   $88.8407   $88.84   $88.85   $88.80  
  7 purchase totals = $932.81       $1,033.3888   $1,033.37   $1,033.35   $1,033.30