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 $216.79   11.543%   $241.8141   $241.81   $241.80   $241.80  
  Purchase #2 $76.79   12.335%   $86.262   $86.26   $86.25   $86.30  
  Purchase #3 $41.64   4.626%   $43.5663   $43.57   $43.55   $43.60  
  Purchase #4 $52.75   11.739%   $58.9423   $58.94   $58.95   $58.90  
  Purchase #5 $170.60   13.133%   $193.0049   $193.00   $193.00   $193.00  
  Purchase #6 $233.57   6.468%   $248.6773   $248.68   $248.70   $248.70  
  Purchase #7 $99.72   4.303%   $104.011   $104.01   $104.00   $104.00  
  7 purchase totals = $891.86       $976.2779   $976.27   $976.25   $976.30