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 $33.89   12.222%   $38.032   $38.03   $38.05   $38.00  
  Purchase #2 $199.37   6.346%   $212.022   $212.02   $212.00   $212.00  
  Purchase #3 $58.71   11.647%   $65.548   $65.55   $65.55   $65.50  
  Purchase #4 $32.64   9.150%   $35.6266   $35.63   $35.65   $35.60  
  Purchase #5 $96.71   13.347%   $109.6179   $109.62   $109.60   $109.60  
  Purchase #6 $10.87   3.428%   $11.2426   $11.24   $11.25   $11.20  
  Purchase #7 $109.40   8.629%   $118.8401   $118.84   $118.85   $118.80  
  7 purchase totals = $541.59       $590.9292   $590.93   $590.95   $590.70