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 $49.48   8.128%   $53.5017   $53.50   $53.50   $53.50  
  Purchase #2 $250.87   7.187%   $268.9   $268.90   $268.90   $268.90  
  Purchase #3 $170.48   4.104%   $177.4765   $177.48   $177.50   $177.50  
  Purchase #4 $83.94   13.231%   $95.0461   $95.05   $95.05   $95.00  
  Purchase #5 $246.75   10.772%   $273.3299   $273.33   $273.35   $273.30  
  Purchase #6 $116.65   7.474%   $125.3684   $125.37   $125.35   $125.40  
  Purchase #7 $107.64   9.766%   $118.1521   $118.15   $118.15   $118.20  
  7 purchase totals = $1,025.81       $1,111.7747   $1,111.78   $1,111.80   $1,111.80