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 $236.55   11.300%   $263.2802   $263.28   $263.30   $263.30  
  Purchase #2 $96.44   7.683%   $103.8495   $103.85   $103.85   $103.80  
  Purchase #3 $48.73   7.265%   $52.2702   $52.27   $52.25   $52.30  
  Purchase #4 $193.84   9.387%   $212.0358   $212.04   $212.05   $212.00  
  Purchase #5 $215.80   8.711%   $234.5983   $234.60   $234.60   $234.60  
  Purchase #6 $44.41   6.506%   $47.2993   $47.30   $47.30   $47.30  
  Purchase #7 $50.46   4.830%   $52.8972   $52.90   $52.90   $52.90  
  7 purchase totals = $886.23       $966.2305   $966.24   $966.25   $966.20