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 $141.99   10.243%   $156.534   $156.53   $156.55   $156.50  
  Purchase #2 $113.54   11.796%   $126.9332   $126.93   $126.95   $126.90  
  Purchase #3 $18.96   11.462%   $21.1332   $21.13   $21.15   $21.10  
  Purchase #4 $212.96   3.654%   $220.7416   $220.74   $220.75   $220.70  
  Purchase #5 $171.57   6.560%   $182.825   $182.83   $182.85   $182.80  
  Purchase #6 $69.45   5.851%   $73.5135   $73.51   $73.50   $73.50  
  Purchase #7 $232.31   12.787%   $262.0155   $262.02   $262.00   $262.00  
  7 purchase totals = $960.78       $1,043.6960   $1,043.69   $1,043.75   $1,043.50