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 $60.77   8.750%   $66.0874   $66.09   $66.10   $66.10  
  Purchase #2 $153.79   13.164%   $174.0349   $174.03   $174.05   $174.00  
  Purchase #3 $153.83   9.793%   $168.8946   $168.89   $168.90   $168.90  
  Purchase #4 $65.52   6.238%   $69.6071   $69.61   $69.60   $69.60  
  Purchase #5 $89.28   5.189%   $93.9127   $93.91   $93.90   $93.90  
  Purchase #6 $222.31   13.717%   $252.8043   $252.80   $252.80   $252.80  
  Purchase #7 $207.88   4.207%   $216.6255   $216.63   $216.65   $216.60  
  7 purchase totals = $953.38       $1,041.9665   $1,041.96   $1,042.00   $1,041.90