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 $129.60   13.187%   $146.6904   $146.69   $146.70   $146.70  
  Purchase #2 $87.51   5.624%   $92.4316   $92.43   $92.45   $92.40  
  Purchase #3 $47.90   6.453%   $50.991   $50.99   $51.00   $51.00  
  Purchase #4 $24.39   9.146%   $26.6207   $26.62   $26.60   $26.60  
  Purchase #5 $228.67   10.156%   $251.8937   $251.89   $251.90   $251.90  
  Purchase #6 $213.94   13.526%   $242.8775   $242.88   $242.90   $242.90  
  Purchase #7 $182.55   5.835%   $193.2018   $193.20   $193.20   $193.20  
  7 purchase totals = $914.56       $1,004.7067   $1,004.70   $1,004.75   $1,004.70