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 $92.25   11.248%   $102.6263   $102.63   $102.65   $102.60  
  Purchase #2 $94.71   12.503%   $106.5516   $106.55   $106.55   $106.60  
  Purchase #3 $58.54   12.630%   $65.9336   $65.93   $65.95   $65.90  
  Purchase #4 $63.36   4.655%   $66.3094   $66.31   $66.30   $66.30  
  Purchase #5 $100.46   5.545%   $106.0305   $106.03   $106.05   $106.00  
  Purchase #6 $10.81   3.109%   $11.1461   $11.15   $11.15   $11.10  
  Purchase #7 $185.95   9.141%   $202.9477   $202.95   $202.95   $202.90  
  7 purchase totals = $606.08       $661.5452   $661.55   $661.60   $661.40