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 $83.62   10.246%   $92.1877   $92.19   $92.20   $92.20  
  Purchase #2 $184.46   9.668%   $202.2936   $202.29   $202.30   $202.30  
  Purchase #3 $69.51   10.253%   $76.6369   $76.64   $76.65   $76.60  
  Purchase #4 $5.40   6.810%   $5.7677   $5.77   $5.75   $5.80  
  Purchase #5 $105.44   6.359%   $112.1449   $112.14   $112.15   $112.10  
  Purchase #6 $126.46   7.156%   $135.5095   $135.51   $135.50   $135.50  
  Purchase #7 $174.90   9.576%   $191.6484   $191.65   $191.65   $191.60  
  7 purchase totals = $749.79       $816.1887   $816.19   $816.20   $816.10