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 $24.97   3.733%   $25.9021   $25.90   $25.90   $25.90  
  Purchase #2 $141.32   10.459%   $156.1007   $156.10   $156.10   $156.10  
  Purchase #3 $149.66   11.366%   $166.6704   $166.67   $166.65   $166.70  
  Purchase #4 $114.90   12.663%   $129.4498   $129.45   $129.45   $129.40  
  Purchase #5 $195.68   13.273%   $221.6526   $221.65   $221.65   $221.70  
  Purchase #6 $106.78   11.125%   $118.6593   $118.66   $118.65   $118.70  
  Purchase #7 $174.86   4.177%   $182.1639   $182.16   $182.15   $182.20  
  7 purchase totals = $908.17       $1,000.5988   $1,000.59   $1,000.55   $1,000.70