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 $143.85   12.616%   $161.9981   $162.00   $162.00   $162.00  
  Purchase #2 $120.98   10.339%   $133.4881   $133.49   $133.50   $133.50  
  Purchase #3 $138.37   8.349%   $149.9225   $149.92   $149.90   $149.90  
  Purchase #4 $168.38   8.620%   $182.8944   $182.89   $182.90   $182.90  
  Purchase #5 $62.42   12.252%   $70.0677   $70.07   $70.05   $70.10  
  Purchase #6 $157.29   6.354%   $167.2842   $167.28   $167.30   $167.30  
  Purchase #7 $94.59   7.723%   $101.8952   $101.90   $101.90   $101.90  
  7 purchase totals = $885.88       $967.5502   $967.55   $967.55   $967.60