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 $119.52   6.772%   $127.6139   $127.61   $127.60   $127.60  
  Purchase #2 $145.37   10.567%   $160.7312   $160.73   $160.75   $160.70  
  Purchase #3 $140.84   8.661%   $153.0382   $153.04   $153.05   $153.00  
  Purchase #4 $221.71   6.811%   $236.8107   $236.81   $236.80   $236.80  
  Purchase #5 $197.89   7.252%   $212.241   $212.24   $212.25   $212.20  
  Purchase #6 $23.49   12.535%   $26.4345   $26.43   $26.45   $26.40  
  Purchase #7 $186.89   10.553%   $206.6125   $206.61   $206.60   $206.60  
  7 purchase totals = $1,035.71       $1,123.4820   $1,123.47   $1,123.50   $1,123.30