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 $175.45   5.856%   $185.7244   $185.72   $185.70   $185.70  
  Purchase #2 $55.79   9.133%   $60.8853   $60.89   $60.90   $60.90  
  Purchase #3 $98.96   8.713%   $107.5824   $107.58   $107.60   $107.60  
  Purchase #4 $32.27   7.854%   $34.8045   $34.80   $34.80   $34.80  
  Purchase #5 $193.92   8.772%   $210.9307   $210.93   $210.95   $210.90  
  Purchase #6 $191.38   12.635%   $215.5609   $215.56   $215.55   $215.60  
  Purchase #7 $25.42   7.862%   $27.4185   $27.42   $27.40   $27.40  
  7 purchase totals = $773.19       $842.9067   $842.90   $842.90   $842.90