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 $88.66   7.208%   $95.0506   $95.05   $95.05   $95.10  
  Purchase #2 $46.85   10.382%   $51.714   $51.71   $51.70   $51.70  
  Purchase #3 $18.66   11.221%   $20.7538   $20.75   $20.75   $20.80  
  Purchase #4 $149.35   9.489%   $163.5218   $163.52   $163.50   $163.50  
  Purchase #5 $73.68   13.522%   $83.643   $83.64   $83.65   $83.60  
  Purchase #6 $10.43   3.321%   $10.7764   $10.78   $10.80   $10.80  
  Purchase #7 $101.73   4.655%   $106.4655   $106.47   $106.45   $106.50  
  7 purchase totals = $489.36       $531.9251   $531.92   $531.90   $532.00