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 $92.81   7.238%   $99.5276   $99.53   $99.55   $99.50  
  Purchase #2 $136.62   3.766%   $141.7651   $141.77   $141.75   $141.80  
  Purchase #3 $97.40   3.390%   $100.7019   $100.70   $100.70   $100.70  
  Purchase #4 $119.55   13.109%   $135.2218   $135.22   $135.20   $135.20  
  Purchase #5 $183.74   6.424%   $195.5435   $195.54   $195.55   $195.50  
  Purchase #6 $67.28   3.251%   $69.4673   $69.47   $69.45   $69.50  
  Purchase #7 $87.96   4.341%   $91.7783   $91.78   $91.80   $91.80  
  7 purchase totals = $785.36       $834.0055   $834.01   $834.00   $834.00