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 $105.68   12.852%   $119.262   $119.26   $119.25   $119.30  
  Purchase #2 $61.27   8.742%   $66.6262   $66.63   $66.65   $66.60  
  Purchase #3 $115.76   4.571%   $121.0514   $121.05   $121.05   $121.10  
  Purchase #4 $9.90   11.433%   $11.0319   $11.03   $11.05   $11.00  
  Purchase #5 $194.61   12.599%   $219.1289   $219.13   $219.15   $219.10  
  Purchase #6 $194.88   3.371%   $201.4494   $201.45   $201.45   $201.40  
  Purchase #7 $243.98   9.656%   $267.5387   $267.54   $267.55   $267.50  
  7 purchase totals = $926.08       $1,006.0885   $1,006.09   $1,006.15   $1,006.00