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 $61.81   11.227%   $68.7494   $68.75   $68.75   $68.70  
  Purchase #2 $217.52   10.383%   $240.1051   $240.11   $240.10   $240.10  
  Purchase #3 $168.60   4.503%   $176.1921   $176.19   $176.20   $176.20  
  Purchase #4 $27.91   10.244%   $30.7691   $30.77   $30.75   $30.80  
  Purchase #5 $104.64   9.320%   $114.3924   $114.39   $114.40   $114.40  
  Purchase #6 $147.72   10.345%   $163.0016   $163.00   $163.00   $163.00  
  Purchase #7 $143.71   3.108%   $148.1765   $148.18   $148.20   $148.20  
  7 purchase totals = $871.91       $941.3862   $941.39   $941.40   $941.40