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 $14.58   13.609%   $16.5642   $16.56   $16.55   $16.60  
  Purchase #2 $44.85   5.230%   $47.1957   $47.20   $47.20   $47.20  
  Purchase #3 $181.87   8.224%   $196.827   $196.83   $196.85   $196.80  
  Purchase #4 $108.96   11.476%   $121.4642   $121.46   $121.45   $121.50  
  Purchase #5 $226.63   8.190%   $245.191   $245.19   $245.20   $245.20  
  Purchase #6 $39.95   10.453%   $44.126   $44.13   $44.15   $44.10  
  Purchase #7 $170.88   10.168%   $188.2551   $188.26   $188.25   $188.30  
  7 purchase totals = $787.72       $859.6232   $859.63   $859.65   $859.70