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 $69.43   8.162%   $75.0969   $75.10   $75.10   $75.10  
  Purchase #2 $92.81   5.378%   $97.8013   $97.80   $97.80   $97.80  
  Purchase #3 $156.42   9.649%   $171.513   $171.51   $171.50   $171.50  
  Purchase #4 $154.58   13.381%   $175.2643   $175.26   $175.25   $175.30  
  Purchase #5 $179.84   4.303%   $187.5785   $187.58   $187.60   $187.60  
  Purchase #6 $100.46   4.455%   $104.9355   $104.94   $104.95   $104.90  
  Purchase #7 $232.42   4.409%   $242.6674   $242.67   $242.65   $242.70  
  7 purchase totals = $985.96       $1,054.8569   $1,054.86   $1,054.85   $1,054.90