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 $119.93   5.102%   $126.0488   $126.05   $126.05   $126.00  
  Purchase #2 $183.61   10.817%   $203.4711   $203.47   $203.45   $203.50  
  Purchase #3 $150.57   5.582%   $158.9748   $158.97   $158.95   $159.00  
  Purchase #4 $142.39   12.284%   $159.8812   $159.88   $159.90   $159.90  
  Purchase #5 $55.58   12.858%   $62.7265   $62.73   $62.75   $62.70  
  Purchase #6 $26.31   10.478%   $29.0668   $29.07   $29.05   $29.10  
  Purchase #7 $14.58   12.779%   $16.4432   $16.44   $16.45   $16.40  
  7 purchase totals = $692.97       $756.6124   $756.61   $756.60   $756.60