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 $92.44   12.510%   $104.0042   $104.00   $104.00   $104.00  
  Purchase #2 $164.93   10.623%   $182.4505   $182.45   $182.45   $182.50  
  Purchase #3 $151.55   6.364%   $161.1946   $161.19   $161.20   $161.20  
  Purchase #4 $66.89   5.431%   $70.5228   $70.52   $70.50   $70.50  
  Purchase #5 $55.49   3.777%   $57.5859   $57.59   $57.60   $57.60  
  Purchase #6 $150.99   11.872%   $168.9155   $168.92   $168.90   $168.90  
  Purchase #7 $247.32   12.669%   $278.653   $278.65   $278.65   $278.70  
  7 purchase totals = $929.61       $1,023.3265   $1,023.32   $1,023.30   $1,023.40