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 $148.57   5.707%   $157.0489   $157.05   $157.05   $157.00  
  Purchase #2 $249.54   7.127%   $267.3247   $267.32   $267.30   $267.30  
  Purchase #3 $23.93   11.481%   $26.6774   $26.68   $26.70   $26.70  
  Purchase #4 $103.86   9.261%   $113.4785   $113.48   $113.50   $113.50  
  Purchase #5 $65.89   4.304%   $68.7259   $68.73   $68.75   $68.70  
  Purchase #6 $111.26   11.605%   $124.1717   $124.17   $124.15   $124.20  
  Purchase #7 $218.55   11.792%   $244.3214   $244.32   $244.30   $244.30  
  7 purchase totals = $921.60       $1,001.7485   $1,001.75   $1,001.75   $1,001.70