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 $94.78   12.843%   $106.9526   $106.95   $106.95   $107.00  
  Purchase #2 $92.68   12.102%   $103.8961   $103.90   $103.90   $103.90  
  Purchase #3 $83.32   12.206%   $93.49   $93.49   $93.50   $93.50  
  Purchase #4 $102.30   4.354%   $106.7541   $106.75   $106.75   $106.80  
  Purchase #5 $148.78   5.673%   $157.2203   $157.22   $157.20   $157.20  
  Purchase #6 $109.75   5.123%   $115.3725   $115.37   $115.35   $115.40  
  Purchase #7 $107.54   8.250%   $116.4121   $116.41   $116.40   $116.40  
  7 purchase totals = $739.15       $800.0977   $800.09   $800.05   $800.20