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 $142.61   5.797%   $150.8771   $150.88   $150.90   $150.90  
  Purchase #2 $70.28   3.500%   $72.7398   $72.74   $72.75   $72.70  
  Purchase #3 $229.73   3.754%   $238.3541   $238.35   $238.35   $238.40  
  Purchase #4 $138.40   3.384%   $143.0835   $143.08   $143.10   $143.10  
  Purchase #5 $27.39   3.574%   $28.3689   $28.37   $28.35   $28.40  
  Purchase #6 $16.44   13.789%   $18.7069   $18.71   $18.70   $18.70  
  Purchase #7 $183.95   7.571%   $197.8769   $197.88   $197.90   $197.90  
  7 purchase totals = $808.80       $850.0072   $850.01   $850.05   $850.10