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 $232.87   3.847%   $241.8285   $241.83   $241.85   $241.80  
  Purchase #2 $70.96   6.574%   $75.6249   $75.62   $75.60   $75.60  
  Purchase #3 $66.85   9.828%   $73.42   $73.42   $73.40   $73.40  
  Purchase #4 $143.34   8.535%   $155.5741   $155.57   $155.55   $155.60  
  Purchase #5 $194.40   6.152%   $206.3595   $206.36   $206.35   $206.40  
  Purchase #6 $71.42   6.449%   $76.0259   $76.03   $76.05   $76.00  
  Purchase #7 $167.88   9.329%   $183.5415   $183.54   $183.55   $183.50  
  7 purchase totals = $947.72       $1,012.3744   $1,012.37   $1,012.35   $1,012.30