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 $68.47   8.361%   $74.1948   $74.19   $74.20   $74.20  
  Purchase #2 $153.27   6.708%   $163.5514   $163.55   $163.55   $163.60  
  Purchase #3 $241.38   11.558%   $269.2787   $269.28   $269.30   $269.30  
  Purchase #4 $79.95   7.460%   $85.9143   $85.91   $85.90   $85.90  
  Purchase #5 $201.26   12.454%   $226.3249   $226.32   $226.30   $226.30  
  Purchase #6 $116.93   10.176%   $128.8288   $128.83   $128.85   $128.80  
  Purchase #7 $124.52   11.873%   $139.3043   $139.30   $139.30   $139.30  
  7 purchase totals = $985.78       $1,087.3972   $1,087.38   $1,087.40   $1,087.40