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 $67.79   13.373%   $76.8556   $76.86   $76.85   $76.90  
  Purchase #2 $149.32   8.140%   $161.4746   $161.47   $161.45   $161.50  
  Purchase #3 $97.35   8.795%   $105.9119   $105.91   $105.90   $105.90  
  Purchase #4 $94.69   12.735%   $106.7488   $106.75   $106.75   $106.70  
  Purchase #5 $135.37   11.248%   $150.5964   $150.60   $150.60   $150.60  
  Purchase #6 $174.42   8.388%   $189.0503   $189.05   $189.05   $189.10  
  Purchase #7 $140.34   10.637%   $155.268   $155.27   $155.25   $155.30  
  7 purchase totals = $859.28       $945.9056   $945.91   $945.85   $946.00