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 $31.91   13.641%   $36.2628   $36.26   $36.25   $36.30  
  Purchase #2 $243.89   8.502%   $264.6255   $264.63   $264.65   $264.60  
  Purchase #3 $148.54   8.355%   $160.9505   $160.95   $160.95   $161.00  
  Purchase #4 $153.32   8.864%   $166.9103   $166.91   $166.90   $166.90  
  Purchase #5 $25.47   6.865%   $27.2185   $27.22   $27.20   $27.20  
  Purchase #6 $86.70   8.780%   $94.3123   $94.31   $94.30   $94.30  
  Purchase #7 $74.85   5.246%   $78.7766   $78.78   $78.80   $78.80  
  7 purchase totals = $764.68       $829.0565   $829.06   $829.05   $829.10