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 $86.63   13.169%   $98.0383   $98.04   $98.05   $98.00  
  Purchase #2 $201.34   7.636%   $216.7143   $216.71   $216.70   $216.70  
  Purchase #3 $153.65   12.336%   $172.6043   $172.60   $172.60   $172.60  
  Purchase #4 $135.59   13.295%   $153.6167   $153.62   $153.60   $153.60  
  Purchase #5 $82.34   6.826%   $87.9605   $87.96   $87.95   $88.00  
  Purchase #6 $140.68   9.568%   $154.1403   $154.14   $154.15   $154.10  
  Purchase #7 $30.68   3.593%   $31.7823   $31.78   $31.80   $31.80  
  7 purchase totals = $830.91       $914.8567   $914.85   $914.85   $914.80