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 $184.89   3.658%   $191.6533   $191.65   $191.65   $191.70  
  Purchase #2 $47.99   13.231%   $54.3396   $54.34   $54.35   $54.30  
  Purchase #3 $167.51   12.246%   $188.0233   $188.02   $188.00   $188.00  
  Purchase #4 $42.56   12.356%   $47.8187   $47.82   $47.80   $47.80  
  Purchase #5 $201.91   10.708%   $223.5305   $223.53   $223.55   $223.50  
  Purchase #6 $173.65   9.187%   $189.6032   $189.60   $189.60   $189.60  
  Purchase #7 $57.80   5.102%   $60.749   $60.75   $60.75   $60.70  
  7 purchase totals = $876.31       $955.7176   $955.71   $955.70   $955.60