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 $6.31   7.815%   $6.8031   $6.80   $6.80   $6.80  
  Purchase #2 $167.35   6.405%   $178.0688   $178.07   $178.05   $178.10  
  Purchase #3 $119.78   10.278%   $132.091   $132.09   $132.10   $132.10  
  Purchase #4 $128.96   4.784%   $135.1294   $135.13   $135.15   $135.10  
  Purchase #5 $164.27   8.345%   $177.9783   $177.98   $178.00   $178.00  
  Purchase #6 $57.39   6.181%   $60.9373   $60.94   $60.95   $60.90  
  Purchase #7 $9.31   12.365%   $10.4612   $10.46   $10.45   $10.50  
  7 purchase totals = $653.37       $701.4691   $701.47   $701.50   $701.50