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 $205.88   12.658%   $231.9403   $231.94   $231.95   $231.90  
  Purchase #2 $174.87   12.498%   $196.7253   $196.73   $196.75   $196.70  
  Purchase #3 $47.28   9.433%   $51.7399   $51.74   $51.75   $51.70  
  Purchase #4 $232.67   9.356%   $254.4386   $254.44   $254.45   $254.40  
  Purchase #5 $124.62   8.196%   $134.8339   $134.83   $134.85   $134.80  
  Purchase #6 $36.38   5.503%   $38.382   $38.38   $38.40   $38.40  
  Purchase #7 $146.61   6.144%   $155.6177   $155.62   $155.60   $155.60  
  7 purchase totals = $968.31       $1,063.6777   $1,063.68   $1,063.75   $1,063.50