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 $32.47   13.697%   $36.9174   $36.92   $36.90   $36.90  
  Purchase #2 $95.61   6.281%   $101.6153   $101.62   $101.60   $101.60  
  Purchase #3 $55.43   8.710%   $60.258   $60.26   $60.25   $60.30  
  Purchase #4 $65.72   7.727%   $70.7982   $70.80   $70.80   $70.80  
  Purchase #5 $181.39   13.536%   $205.943   $205.94   $205.95   $205.90  
  Purchase #6 $224.69   10.206%   $247.6219   $247.62   $247.60   $247.60  
  Purchase #7 $170.31   9.168%   $185.924   $185.92   $185.90   $185.90  
  7 purchase totals = $825.62       $909.0778   $909.08   $909.00   $909.00