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 $73.48   11.848%   $82.1859   $82.19   $82.20   $82.20  
  Purchase #2 $181.47   5.351%   $191.1805   $191.18   $191.20   $191.20  
  Purchase #3 $241.43   11.576%   $269.3779   $269.38   $269.40   $269.40  
  Purchase #4 $203.54   11.482%   $226.9105   $226.91   $226.90   $226.90  
  Purchase #5 $163.84   11.153%   $182.1131   $182.11   $182.10   $182.10  
  Purchase #6 $15.62   8.853%   $17.0028   $17.00   $17.00   $17.00  
  Purchase #7 $38.60   7.754%   $41.593   $41.59   $41.60   $41.60  
  7 purchase totals = $917.98       $1,010.3637   $1,010.36   $1,010.40   $1,010.40