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 $98.85   11.464%   $110.1822   $110.18   $110.20   $110.20  
  Purchase #2 $54.54   4.188%   $56.8241   $56.82   $56.80   $56.80  
  Purchase #3 $245.47   5.469%   $258.8948   $258.89   $258.90   $258.90  
  Purchase #4 $49.98   8.194%   $54.0754   $54.08   $54.10   $54.10  
  Purchase #5 $175.81   11.121%   $195.3618   $195.36   $195.35   $195.40  
  Purchase #6 $167.49   9.215%   $182.9242   $182.92   $182.90   $182.90  
  Purchase #7 $94.62   6.201%   $100.4874   $100.49   $100.50   $100.50  
  7 purchase totals = $886.76       $958.7499   $958.74   $958.75   $958.80