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 $130.43   11.638%   $145.6094   $145.61   $145.60   $145.60  
  Purchase #2 $24.53   9.297%   $26.8106   $26.81   $26.80   $26.80  
  Purchase #3 $24.40   6.116%   $25.8923   $25.89   $25.90   $25.90  
  Purchase #4 $160.47   10.569%   $177.4301   $177.43   $177.45   $177.40  
  Purchase #5 $215.95   5.104%   $226.9721   $226.97   $226.95   $227.00  
  Purchase #6 $247.99   13.596%   $281.7067   $281.71   $281.70   $281.70  
  Purchase #7 $75.95   4.779%   $79.5797   $79.58   $79.60   $79.60  
  7 purchase totals = $879.72       $964.0009   $964.00   $964.00   $964.00