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 $224.42   10.779%   $248.6102   $248.61   $248.60   $248.60  
  Purchase #2 $226.37   9.141%   $247.0625   $247.06   $247.05   $247.10  
  Purchase #3 $25.82   6.155%   $27.4092   $27.41   $27.40   $27.40  
  Purchase #4 $70.99   7.783%   $76.5152   $76.52   $76.50   $76.50  
  Purchase #5 $98.44   10.195%   $108.476   $108.48   $108.50   $108.50  
  Purchase #6 $91.97   13.838%   $104.6968   $104.70   $104.70   $104.70  
  Purchase #7 $207.32   6.628%   $221.0612   $221.06   $221.05   $221.10  
  7 purchase totals = $945.33       $1,033.8311   $1,033.84   $1,033.80   $1,033.90