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 $165.82   12.305%   $186.2242   $186.22   $186.20   $186.20  
  Purchase #2 $85.50   13.387%   $96.9459   $96.95   $96.95   $96.90  
  Purchase #3 $108.84   9.289%   $118.9501   $118.95   $118.95   $119.00  
  Purchase #4 $139.47   3.304%   $144.0781   $144.08   $144.10   $144.10  
  Purchase #5 $198.99   5.799%   $210.5294   $210.53   $210.55   $210.50  
  Purchase #6 $208.50   4.630%   $218.1536   $218.15   $218.15   $218.20  
  Purchase #7 $169.42   5.598%   $178.9041   $178.90   $178.90   $178.90  
  7 purchase totals = $1,076.54       $1,153.7854   $1,153.78   $1,153.80   $1,153.80