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 $173.86   6.265%   $184.7523   $184.75   $184.75   $184.80  
  Purchase #2 $183.69   10.295%   $202.6009   $202.60   $202.60   $202.60  
  Purchase #3 $93.76   13.554%   $106.4682   $106.47   $106.45   $106.50  
  Purchase #4 $95.60   3.107%   $98.5703   $98.57   $98.55   $98.60  
  Purchase #5 $98.55   12.393%   $110.7633   $110.76   $110.75   $110.80  
  Purchase #6 $119.58   8.662%   $129.938   $129.94   $129.95   $129.90  
  Purchase #7 $219.41   7.475%   $235.8109   $235.81   $235.80   $235.80  
  7 purchase totals = $984.45       $1,068.9039   $1,068.90   $1,068.85   $1,069.00