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 $67.36   9.310%   $73.6312   $73.63   $73.65   $73.60  
  Purchase #2 $221.86   5.527%   $234.1222   $234.12   $234.10   $234.10  
  Purchase #3 $91.90   5.629%   $97.0731   $97.07   $97.05   $97.10  
  Purchase #4 $59.52   8.675%   $64.6834   $64.68   $64.70   $64.70  
  Purchase #5 $230.76   8.290%   $249.89   $249.89   $249.90   $249.90  
  Purchase #6 $190.34   12.341%   $213.8299   $213.83   $213.85   $213.80  
  Purchase #7 $127.58   8.227%   $138.076   $138.08   $138.10   $138.10  
  7 purchase totals = $989.32       $1,071.3058   $1,071.30   $1,071.35   $1,071.30