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 $196.56   11.554%   $219.2705   $219.27   $219.25   $219.30  
  Purchase #2 $145.40   9.147%   $158.6997   $158.70   $158.70   $158.70  
  Purchase #3 $58.72   7.737%   $63.2632   $63.26   $63.25   $63.30  
  Purchase #4 $43.26   11.171%   $48.0926   $48.09   $48.10   $48.10  
  Purchase #5 $217.45   4.213%   $226.6112   $226.61   $226.60   $226.60  
  Purchase #6 $51.64   7.354%   $55.4376   $55.44   $55.45   $55.40  
  Purchase #7 $233.48   7.218%   $250.3326   $250.33   $250.35   $250.30  
  7 purchase totals = $946.51       $1,021.7074   $1,021.70   $1,021.70   $1,021.70