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 $220.87   11.462%   $246.1861   $246.19   $246.20   $246.20  
  Purchase #2 $124.96   13.798%   $142.202   $142.20   $142.20   $142.20  
  Purchase #3 $77.70   12.870%   $87.7   $87.70   $87.70   $87.70  
  Purchase #4 $30.78   13.170%   $34.8337   $34.83   $34.85   $34.80  
  Purchase #5 $73.41   11.618%   $81.9388   $81.94   $81.95   $81.90  
  Purchase #6 $237.31   7.394%   $254.8567   $254.86   $254.85   $254.90  
  Purchase #7 $183.88   7.483%   $197.6397   $197.64   $197.65   $197.60  
  7 purchase totals = $948.91       $1,045.3570   $1,045.36   $1,045.40   $1,045.30