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 $29.83   7.381%   $32.0318   $32.03   $32.05   $32.00  
  Purchase #2 $156.29   11.581%   $174.3899   $174.39   $174.40   $174.40  
  Purchase #3 $65.66   3.174%   $67.744   $67.74   $67.75   $67.70  
  Purchase #4 $163.69   9.323%   $178.9508   $178.95   $178.95   $179.00  
  Purchase #5 $229.91   9.350%   $251.4066   $251.41   $251.40   $251.40  
  Purchase #6 $128.25   3.551%   $132.8042   $132.80   $132.80   $132.80  
  Purchase #7 $60.42   11.602%   $67.4299   $67.43   $67.45   $67.40  
  7 purchase totals = $834.05       $904.7572   $904.75   $904.80   $904.70