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 $114.94   6.742%   $122.6893   $122.69   $122.70   $122.70  
  Purchase #2 $249.30   5.510%   $263.0364   $263.04   $263.05   $263.00  
  Purchase #3 $221.96   8.791%   $241.4725   $241.47   $241.45   $241.50  
  Purchase #4 $81.52   12.335%   $91.5755   $91.58   $91.60   $91.60  
  Purchase #5 $11.94   11.638%   $13.3296   $13.33   $13.35   $13.30  
  Purchase #6 $234.33   8.538%   $254.3371   $254.34   $254.35   $254.30  
  Purchase #7 $160.32   10.137%   $176.5716   $176.57   $176.55   $176.60  
  7 purchase totals = $1,074.31       $1,163.0120   $1,163.02   $1,163.05   $1,163.00