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 $96.72   8.284%   $104.7323   $104.73   $104.75   $104.70  
  Purchase #2 $21.81   4.419%   $22.7738   $22.77   $22.75   $22.80  
  Purchase #3 $155.92   7.497%   $167.6093   $167.61   $167.60   $167.60  
  Purchase #4 $46.39   8.718%   $50.4343   $50.43   $50.45   $50.40  
  Purchase #5 $228.84   9.264%   $250.0397   $250.04   $250.05   $250.00  
  Purchase #6 $48.83   3.798%   $50.6846   $50.68   $50.70   $50.70  
  Purchase #7 $237.71   6.627%   $253.463   $253.46   $253.45   $253.50  
  7 purchase totals = $836.22       $899.7370   $899.72   $899.75   $899.70