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 $160.94   4.117%   $167.5659   $167.57   $167.55   $167.60  
  Purchase #2 $177.63   13.582%   $201.7557   $201.76   $201.75   $201.80  
  Purchase #3 $35.83   7.222%   $38.4176   $38.42   $38.40   $38.40  
  Purchase #4 $230.57   13.710%   $262.1811   $262.18   $262.20   $262.20  
  Purchase #5 $68.86   6.113%   $73.0694   $73.07   $73.05   $73.10  
  Purchase #6 $145.97   13.533%   $165.7241   $165.72   $165.70   $165.70  
  Purchase #7 $175.30   11.244%   $195.0107   $195.01   $195.00   $195.00  
  7 purchase totals = $995.10       $1,103.7245   $1,103.73   $1,103.65   $1,103.80