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 $34.96   3.493%   $36.1812   $36.18   $36.20   $36.20  
  Purchase #2 $176.52   11.138%   $196.1808   $196.18   $196.20   $196.20  
  Purchase #3 $243.90   5.750%   $257.9243   $257.92   $257.90   $257.90  
  Purchase #4 $163.68   11.154%   $181.9369   $181.94   $181.95   $181.90  
  Purchase #5 $141.41   5.286%   $148.8849   $148.88   $148.90   $148.90  
  Purchase #6 $95.25   3.760%   $98.8314   $98.83   $98.85   $98.80  
  Purchase #7 $19.40   5.595%   $20.4854   $20.49   $20.50   $20.50  
  7 purchase totals = $875.12       $940.4249   $940.42   $940.50   $940.40