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 $22.58   8.244%   $24.4415   $24.44   $24.45   $24.40  
  Purchase #2 $98.34   12.163%   $110.3011   $110.30   $110.30   $110.30  
  Purchase #3 $86.43   11.342%   $96.2329   $96.23   $96.25   $96.20  
  Purchase #4 $139.46   10.717%   $154.4059   $154.41   $154.40   $154.40  
  Purchase #5 $72.37   13.297%   $81.993   $81.99   $82.00   $82.00  
  Purchase #6 $129.57   3.276%   $133.8147   $133.81   $133.80   $133.80  
  Purchase #7 $148.28   3.841%   $153.9754   $153.98   $154.00   $154.00  
  7 purchase totals = $697.03       $755.1645   $755.16   $755.20   $755.10