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 $69.99   5.614%   $73.9192   $73.92   $73.90   $73.90  
  Purchase #2 $182.71   7.705%   $196.7878   $196.79   $196.80   $196.80  
  Purchase #3 $60.74   8.582%   $65.9527   $65.95   $65.95   $66.00  
  Purchase #4 $159.37   6.250%   $169.3306   $169.33   $169.35   $169.30  
  Purchase #5 $38.36   8.104%   $41.4687   $41.47   $41.45   $41.50  
  Purchase #6 $120.45   4.769%   $126.1943   $126.19   $126.20   $126.20  
  Purchase #7 $72.66   3.137%   $74.9393   $74.94   $74.95   $74.90  
  7 purchase totals = $704.28       $748.5926   $748.59   $748.60   $748.60