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 $161.97   9.112%   $176.7287   $176.73   $176.75   $176.70  
  Purchase #2 $156.73   13.779%   $178.3258   $178.33   $178.35   $178.30  
  Purchase #3 $32.72   3.690%   $33.9274   $33.93   $33.95   $33.90  
  Purchase #4 $218.91   7.336%   $234.9692   $234.97   $234.95   $235.00  
  Purchase #5 $49.28   8.786%   $53.6097   $53.61   $53.60   $53.60  
  Purchase #6 $215.90   11.133%   $239.9361   $239.94   $239.95   $239.90  
  Purchase #7 $30.57   6.148%   $32.4494   $32.45   $32.45   $32.40  
  7 purchase totals = $866.08       $949.9463   $949.96   $950.00   $949.80