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 $62.72   3.702%   $65.0419   $65.04   $65.05   $65.00  
  Purchase #2 $128.37   9.762%   $140.9015   $140.90   $140.90   $140.90  
  Purchase #3 $69.47   4.634%   $72.6892   $72.69   $72.70   $72.70  
  Purchase #4 $231.43   3.560%   $239.6689   $239.67   $239.65   $239.70  
  Purchase #5 $153.62   12.761%   $173.2234   $173.22   $173.20   $173.20  
  Purchase #6 $53.68   9.196%   $58.6164   $58.62   $58.60   $58.60  
  Purchase #7 $181.34   9.154%   $197.9399   $197.94   $197.95   $197.90  
  7 purchase totals = $880.63       $948.0812   $948.08   $948.05   $948.00