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 $103.58   12.361%   $116.3835   $116.38   $116.40   $116.40  
  Purchase #2 $212.86   13.529%   $241.6578   $241.66   $241.65   $241.70  
  Purchase #3 $180.47   4.627%   $188.8203   $188.82   $188.80   $188.80  
  Purchase #4 $220.89   8.535%   $239.743   $239.74   $239.75   $239.70  
  Purchase #5 $153.88   11.578%   $171.6962   $171.70   $171.70   $171.70  
  Purchase #6 $121.47   13.461%   $137.8211   $137.82   $137.80   $137.80  
  Purchase #7 $51.46   13.295%   $58.3016   $58.30   $58.30   $58.30  
  7 purchase totals = $1,044.61       $1,154.4235   $1,154.42   $1,154.40   $1,154.40