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 $61.37   3.685%   $63.6315   $63.63   $63.65   $63.60  
  Purchase #2 $95.57   6.198%   $101.4934   $101.49   $101.50   $101.50  
  Purchase #3 $48.76   4.270%   $50.8421   $50.84   $50.85   $50.80  
  Purchase #4 $121.83   10.832%   $135.0266   $135.03   $135.05   $135.00  
  Purchase #5 $166.60   10.845%   $184.6678   $184.67   $184.65   $184.70  
  Purchase #6 $192.63   5.388%   $203.0089   $203.01   $203.00   $203.00  
  Purchase #7 $64.76   3.589%   $67.0842   $67.08   $67.10   $67.10  
  7 purchase totals = $751.52       $805.7545   $805.75   $805.80   $805.70