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 $111.83   12.859%   $126.2102   $126.21   $126.20   $126.20  
  Purchase #2 $185.82   6.184%   $197.3111   $197.31   $197.30   $197.30  
  Purchase #3 $63.73   6.257%   $67.7176   $67.72   $67.70   $67.70  
  Purchase #4 $143.45   8.871%   $156.1754   $156.18   $156.20   $156.20  
  Purchase #5 $154.39   13.633%   $175.438   $175.44   $175.45   $175.40  
  Purchase #6 $41.48   7.870%   $44.7445   $44.74   $44.75   $44.70  
  Purchase #7 $216.95   7.442%   $233.0954   $233.10   $233.10   $233.10  
  7 purchase totals = $917.65       $1,000.6922   $1,000.70   $1,000.70   $1,000.60