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 $185.89   11.214%   $206.7357   $206.74   $206.75   $206.70  
  Purchase #2 $136.80   11.662%   $152.7536   $152.75   $152.75   $152.80  
  Purchase #3 $81.75   7.151%   $87.5959   $87.60   $87.60   $87.60  
  Purchase #4 $54.47   8.145%   $58.9066   $58.91   $58.90   $58.90  
  Purchase #5 $128.32   7.159%   $137.5064   $137.51   $137.50   $137.50  
  Purchase #6 $203.92   11.865%   $228.1151   $228.12   $228.10   $228.10  
  Purchase #7 $141.57   7.558%   $152.2699   $152.27   $152.25   $152.30  
  7 purchase totals = $932.72       $1,023.8832   $1,023.90   $1,023.85   $1,023.90