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 $29.42   11.650%   $32.8474   $32.85   $32.85   $32.80  
  Purchase #2 $239.26   8.580%   $259.7885   $259.79   $259.80   $259.80  
  Purchase #3 $73.83   8.106%   $79.8147   $79.81   $79.80   $79.80  
  Purchase #4 $23.89   10.353%   $26.3633   $26.36   $26.35   $26.40  
  Purchase #5 $114.84   6.489%   $122.292   $122.29   $122.30   $122.30  
  Purchase #6 $53.30   10.487%   $58.8896   $58.89   $58.90   $58.90  
  Purchase #7 $247.82   13.585%   $281.4863   $281.49   $281.50   $281.50  
  7 purchase totals = $782.36       $861.4818   $861.48   $861.50   $861.50