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 $94.98   7.678%   $102.2726   $102.27   $102.25   $102.30  
  Purchase #2 $166.38   11.605%   $185.6884   $185.69   $185.70   $185.70  
  Purchase #3 $232.96   10.311%   $256.9805   $256.98   $257.00   $257.00  
  Purchase #4 $137.76   11.327%   $153.3641   $153.36   $153.35   $153.40  
  Purchase #5 $71.40   12.347%   $80.2158   $80.22   $80.20   $80.20  
  Purchase #6 $143.31   9.271%   $156.5963   $156.60   $156.60   $156.60  
  Purchase #7 $222.47   11.799%   $248.7192   $248.72   $248.70   $248.70  
  7 purchase totals = $1,069.26       $1,183.8369   $1,183.84   $1,183.80   $1,183.90