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 $162.99   9.713%   $178.8212   $178.82   $178.80   $178.80  
  Purchase #2 $81.72   12.757%   $92.145   $92.15   $92.15   $92.10  
  Purchase #3 $68.65   11.827%   $76.7692   $76.77   $76.75   $76.80  
  Purchase #4 $128.82   3.691%   $133.5747   $133.57   $133.55   $133.60  
  Purchase #5 $162.40   10.746%   $179.8515   $179.85   $179.85   $179.90  
  Purchase #6 $27.31   13.310%   $30.945   $30.95   $30.95   $30.90  
  Purchase #7 $152.90   13.812%   $174.0185   $174.02   $174.00   $174.00  
  7 purchase totals = $784.79       $866.1251   $866.13   $866.05   $866.10