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 $67.97   8.763%   $73.9262   $73.93   $73.95   $73.90  
  Purchase #2 $134.49   10.757%   $148.9571   $148.96   $148.95   $149.00  
  Purchase #3 $249.97   12.555%   $281.3537   $281.35   $281.35   $281.40  
  Purchase #4 $148.93   3.566%   $154.2408   $154.24   $154.25   $154.20  
  Purchase #5 $180.30   3.376%   $186.3869   $186.39   $186.40   $186.40  
  Purchase #6 $83.39   8.339%   $90.3439   $90.34   $90.35   $90.30  
  Purchase #7 $110.43   11.426%   $123.0477   $123.05   $123.05   $123.00  
  7 purchase totals = $975.48       $1,058.2563   $1,058.26   $1,058.30   $1,058.20