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 $246.35   6.768%   $263.023   $263.02   $263.00   $263.00  
  Purchase #2 $150.67   3.405%   $155.8003   $155.80   $155.80   $155.80  
  Purchase #3 $57.77   7.363%   $62.0236   $62.02   $62.00   $62.00  
  Purchase #4 $221.97   11.785%   $248.1292   $248.13   $248.15   $248.10  
  Purchase #5 $38.80   3.512%   $40.1627   $40.16   $40.15   $40.20  
  Purchase #6 $141.50   10.244%   $155.9953   $156.00   $156.00   $156.00  
  Purchase #7 $193.38   6.674%   $206.2862   $206.29   $206.30   $206.30  
  7 purchase totals = $1,050.44       $1,131.4203   $1,131.42   $1,131.40   $1,131.40