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 $244.79   8.264%   $265.0194   $265.02   $265.00   $265.00  
  Purchase #2 $247.25   5.140%   $259.9587   $259.96   $259.95   $260.00  
  Purchase #3 $67.95   8.396%   $73.6551   $73.66   $73.65   $73.70  
  Purchase #4 $51.45   12.419%   $57.8396   $57.84   $57.85   $57.80  
  Purchase #5 $177.59   9.751%   $194.9068   $194.91   $194.90   $194.90  
  Purchase #6 $209.51   7.865%   $225.988   $225.99   $226.00   $226.00  
  Purchase #7 $176.89   8.474%   $191.8797   $191.88   $191.90   $191.90  
  7 purchase totals = $1,175.43       $1,269.2473   $1,269.26   $1,269.25   $1,269.30