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 $67.65   12.691%   $76.2355   $76.24   $76.25   $76.20  
  Purchase #2 $202.28   7.391%   $217.2305   $217.23   $217.25   $217.20  
  Purchase #3 $162.29   7.746%   $174.861   $174.86   $174.85   $174.90  
  Purchase #4 $126.54   6.635%   $134.9359   $134.94   $134.95   $134.90  
  Purchase #5 $128.33   9.589%   $140.6356   $140.64   $140.65   $140.60  
  Purchase #6 $94.73   3.462%   $98.0096   $98.01   $98.00   $98.00  
  Purchase #7 $155.29   6.503%   $165.3885   $165.39   $165.40   $165.40  
  7 purchase totals = $937.11       $1,007.2966   $1,007.31   $1,007.35   $1,007.20