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 $247.85   11.166%   $275.5249   $275.52   $275.50   $275.50  
  Purchase #2 $70.50   8.215%   $76.2916   $76.29   $76.30   $76.30  
  Purchase #3 $65.40   9.563%   $71.6542   $71.65   $71.65   $71.70  
  Purchase #4 $105.84   8.163%   $114.4797   $114.48   $114.50   $114.50  
  Purchase #5 $117.32   3.865%   $121.8544   $121.85   $121.85   $121.90  
  Purchase #6 $7.86   11.178%   $8.7386   $8.74   $8.75   $8.70  
  Purchase #7 $52.59   7.814%   $56.6994   $56.70   $56.70   $56.70  
  7 purchase totals = $667.36       $725.2428   $725.23   $725.25   $725.30