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 $62.53   8.676%   $67.9551   $67.96   $67.95   $68.00  
  Purchase #2 $74.58   3.842%   $77.4454   $77.45   $77.45   $77.40  
  Purchase #3 $94.87   11.695%   $105.965   $105.97   $105.95   $106.00  
  Purchase #4 $111.67   11.103%   $124.0687   $124.07   $124.05   $124.10  
  Purchase #5 $101.49   12.307%   $113.9804   $113.98   $114.00   $114.00  
  Purchase #6 $103.47   9.344%   $113.1382   $113.14   $113.15   $113.10  
  Purchase #7 $81.98   7.488%   $88.1187   $88.12   $88.10   $88.10  
  7 purchase totals = $630.59       $690.6715   $690.69   $690.65   $690.70