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 $83.47   12.629%   $94.0114   $94.01   $94.00   $94.00  
  Purchase #2 $56.84   4.644%   $59.4796   $59.48   $59.50   $59.50  
  Purchase #3 $200.74   12.423%   $225.6779   $225.68   $225.70   $225.70  
  Purchase #4 $64.34   5.436%   $67.8375   $67.84   $67.85   $67.80  
  Purchase #5 $118.64   4.594%   $124.0903   $124.09   $124.10   $124.10  
  Purchase #6 $166.66   10.791%   $184.6443   $184.64   $184.65   $184.60  
  Purchase #7 $60.76   5.274%   $63.9645   $63.96   $63.95   $64.00  
  7 purchase totals = $751.45       $819.7055   $819.70   $819.75   $819.70