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 $200.96   11.117%   $223.3007   $223.30   $223.30   $223.30  
  Purchase #2 $233.96   5.511%   $246.8535   $246.85   $246.85   $246.90  
  Purchase #3 $226.39   5.531%   $238.9116   $238.91   $238.90   $238.90  
  Purchase #4 $43.27   12.714%   $48.7713   $48.77   $48.75   $48.80  
  Purchase #5 $148.40   10.409%   $163.847   $163.85   $163.85   $163.80  
  Purchase #6 $250.72   11.660%   $279.954   $279.95   $279.95   $280.00  
  Purchase #7 $24.47   10.745%   $27.0993   $27.10   $27.10   $27.10  
  7 purchase totals = $1,128.17       $1,228.7374   $1,228.73   $1,228.70   $1,228.80