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 $70.86   3.206%   $73.1318   $73.13   $73.15   $73.10  
  Purchase #2 $182.94   10.150%   $201.5084   $201.51   $201.50   $201.50  
  Purchase #3 $88.94   9.266%   $97.1812   $97.18   $97.20   $97.20  
  Purchase #4 $78.69   6.204%   $83.5719   $83.57   $83.55   $83.60  
  Purchase #5 $157.82   4.176%   $164.4106   $164.41   $164.40   $164.40  
  Purchase #6 $197.42   8.717%   $214.6291   $214.63   $214.65   $214.60  
  Purchase #7 $212.69   7.147%   $227.891   $227.89   $227.90   $227.90  
  7 purchase totals = $989.36       $1,062.3240   $1,062.32   $1,062.35   $1,062.30