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 $59.37   8.768%   $64.5756   $64.58   $64.60   $64.60  
  Purchase #2 $205.98   10.126%   $226.8375   $226.84   $226.85   $226.80  
  Purchase #3 $77.56   13.358%   $87.9205   $87.92   $87.90   $87.90  
  Purchase #4 $248.68   3.364%   $257.0456   $257.05   $257.05   $257.00  
  Purchase #5 $237.35   7.483%   $255.1109   $255.11   $255.10   $255.10  
  Purchase #6 $201.54   11.577%   $224.8723   $224.87   $224.85   $224.90  
  Purchase #7 $65.86   9.630%   $72.2023   $72.20   $72.20   $72.20  
  7 purchase totals = $1,096.34       $1,188.5647   $1,188.57   $1,188.55   $1,188.50