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 $91.81   3.857%   $95.3511   $95.35   $95.35   $95.40  
  Purchase #2 $44.91   10.233%   $49.5056   $49.51   $49.50   $49.50  
  Purchase #3 $229.35   13.185%   $259.5898   $259.59   $259.60   $259.60  
  Purchase #4 $93.46   4.706%   $97.8582   $97.86   $97.85   $97.90  
  Purchase #5 $155.91   5.157%   $163.9503   $163.95   $163.95   $164.00  
  Purchase #6 $140.50   3.411%   $145.2925   $145.29   $145.30   $145.30  
  Purchase #7 $21.53   6.724%   $22.9777   $22.98   $23.00   $23.00  
  7 purchase totals = $777.47       $834.5252   $834.53   $834.55   $834.70