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 $88.66   6.108%   $94.0754   $94.08   $94.10   $94.10  
  Purchase #2 $144.61   4.356%   $150.9092   $150.91   $150.90   $150.90  
  Purchase #3 $111.50   3.286%   $115.1639   $115.16   $115.15   $115.20  
  Purchase #4 $188.48   11.371%   $209.9121   $209.91   $209.90   $209.90  
  Purchase #5 $8.44   9.712%   $9.2597   $9.26   $9.25   $9.30  
  Purchase #6 $229.99   4.321%   $239.9279   $239.93   $239.95   $239.90  
  Purchase #7 $114.98   3.311%   $118.787   $118.79   $118.80   $118.80  
  7 purchase totals = $886.66       $938.0352   $938.04   $938.05   $938.10