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 $34.63   5.705%   $36.6056   $36.61   $36.60   $36.60  
  Purchase #2 $32.39   10.758%   $35.8745   $35.87   $35.85   $35.90  
  Purchase #3 $100.52   11.548%   $112.128   $112.13   $112.15   $112.10  
  Purchase #4 $243.90   12.429%   $274.2143   $274.21   $274.20   $274.20  
  Purchase #5 $87.70   8.778%   $95.3983   $95.40   $95.40   $95.40  
  Purchase #6 $205.42   4.623%   $214.9166   $214.92   $214.90   $214.90  
  Purchase #7 $140.46   7.447%   $150.9201   $150.92   $150.90   $150.90  
  7 purchase totals = $845.02       $920.0574   $920.06   $920.00   $920.00