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 $247.88   4.723%   $259.5874   $259.59   $259.60   $259.60  
  Purchase #2 $210.51   12.107%   $235.9964   $236.00   $236.00   $236.00  
  Purchase #3 $134.53   10.350%   $148.4539   $148.45   $148.45   $148.50  
  Purchase #4 $195.40   5.858%   $206.8465   $206.85   $206.85   $206.80  
  Purchase #5 $198.70   9.498%   $217.5725   $217.57   $217.55   $217.60  
  Purchase #6 $228.81   10.211%   $252.1738   $252.17   $252.15   $252.20  
  Purchase #7 $83.43   12.285%   $93.6794   $93.68   $93.70   $93.70  
  7 purchase totals = $1,299.26       $1,414.3099   $1,414.31   $1,414.30   $1,414.40