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 $118.62   4.412%   $123.8535   $123.85   $123.85   $123.90  
  Purchase #2 $181.64   6.781%   $193.957   $193.96   $193.95   $194.00  
  Purchase #3 $68.77   12.347%   $77.261   $77.26   $77.25   $77.30  
  Purchase #4 $160.86   4.174%   $167.5743   $167.57   $167.55   $167.60  
  Purchase #5 $115.54   9.218%   $126.1905   $126.19   $126.20   $126.20  
  Purchase #6 $153.26   4.381%   $159.9743   $159.97   $159.95   $160.00  
  Purchase #7 $239.38   6.691%   $255.3969   $255.40   $255.40   $255.40  
  7 purchase totals = $1,038.07       $1,104.2075   $1,104.20   $1,104.15   $1,104.40