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 $183.79   9.768%   $201.7426   $201.74   $201.75   $201.70  
  Purchase #2 $118.87   6.193%   $126.2316   $126.23   $126.25   $126.20  
  Purchase #3 $35.41   11.854%   $39.6075   $39.61   $39.60   $39.60  
  Purchase #4 $156.79   9.353%   $171.4546   $171.45   $171.45   $171.50  
  Purchase #5 $102.57   9.264%   $112.0721   $112.07   $112.05   $112.10  
  Purchase #6 $200.95   9.527%   $220.0945   $220.09   $220.10   $220.10  
  Purchase #7 $154.34   7.679%   $166.1918   $166.19   $166.20   $166.20  
  7 purchase totals = $952.72       $1,037.3947   $1,037.38   $1,037.40   $1,037.40