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 $47.28   8.404%   $51.2534   $51.25   $51.25   $51.30  
  Purchase #2 $115.39   6.777%   $123.21   $123.21   $123.20   $123.20  
  Purchase #3 $162.67   7.226%   $174.4245   $174.42   $174.40   $174.40  
  Purchase #4 $205.59   4.405%   $214.6462   $214.65   $214.65   $214.60  
  Purchase #5 $172.49   4.770%   $180.7178   $180.72   $180.70   $180.70  
  Purchase #6 $162.97   3.728%   $169.0455   $169.05   $169.05   $169.00  
  Purchase #7 $78.44   13.297%   $88.8702   $88.87   $88.85   $88.90  
  7 purchase totals = $944.83       $1,002.1676   $1,002.17   $1,002.10   $1,002.10