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 $46.92   3.424%   $48.5265   $48.53   $48.55   $48.50  
  Purchase #2 $107.35   8.597%   $116.5789   $116.58   $116.60   $116.60  
  Purchase #3 $22.70   3.799%   $23.5624   $23.56   $23.55   $23.60  
  Purchase #4 $169.64   4.572%   $177.3959   $177.40   $177.40   $177.40  
  Purchase #5 $166.91   13.336%   $189.1691   $189.17   $189.15   $189.20  
  Purchase #6 $222.28   4.689%   $232.7027   $232.70   $232.70   $232.70  
  Purchase #7 $78.92   8.402%   $85.5509   $85.55   $85.55   $85.60  
  7 purchase totals = $814.72       $873.4864   $873.49   $873.50   $873.60