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 $14.80   11.620%   $16.5198   $16.52   $16.50   $16.50  
  Purchase #2 $114.70   12.783%   $129.3621   $129.36   $129.35   $129.40  
  Purchase #3 $54.73   9.452%   $59.9031   $59.90   $59.90   $59.90  
  Purchase #4 $157.36   3.869%   $163.4483   $163.45   $163.45   $163.40  
  Purchase #5 $57.36   11.599%   $64.0132   $64.01   $64.00   $64.00  
  Purchase #6 $207.86   5.255%   $218.783   $218.78   $218.80   $218.80  
  Purchase #7 $104.30   10.822%   $115.5873   $115.59   $115.60   $115.60  
  7 purchase totals = $711.11       $767.6168   $767.61   $767.60   $767.60