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 $122.77   3.257%   $126.7686   $126.77   $126.75   $126.80  
  Purchase #2 $76.91   10.183%   $84.7417   $84.74   $84.75   $84.70  
  Purchase #3 $88.91   9.545%   $97.3965   $97.40   $97.40   $97.40  
  Purchase #4 $32.60   12.439%   $36.6551   $36.66   $36.65   $36.70  
  Purchase #5 $145.34   5.313%   $153.0619   $153.06   $153.05   $153.10  
  Purchase #6 $177.47   5.279%   $186.8386   $186.84   $186.85   $186.80  
  Purchase #7 $147.84   6.393%   $157.2914   $157.29   $157.30   $157.30  
  7 purchase totals = $791.84       $842.7538   $842.76   $842.75   $842.80