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 $207.72   11.761%   $232.1499   $232.15   $232.15   $232.10  
  Purchase #2 $69.72   13.818%   $79.3539   $79.35   $79.35   $79.40  
  Purchase #3 $172.40   4.734%   $180.5614   $180.56   $180.55   $180.60  
  Purchase #4 $220.51   12.607%   $248.3097   $248.31   $248.30   $248.30  
  Purchase #5 $96.26   5.836%   $101.8777   $101.88   $101.90   $101.90  
  Purchase #6 $239.89   11.301%   $267   $267.00   $267.00   $267.00  
  Purchase #7 $216.47   8.603%   $235.0929   $235.09   $235.10   $235.10  
  7 purchase totals = $1,222.97       $1,344.3455   $1,344.34   $1,344.35   $1,344.40