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 $205.41   3.828%   $213.2731   $213.27   $213.25   $213.30  
  Purchase #2 $56.86   6.228%   $60.4012   $60.40   $60.40   $60.40  
  Purchase #3 $117.59   8.566%   $127.6628   $127.66   $127.65   $127.70  
  Purchase #4 $220.49   3.530%   $228.2733   $228.27   $228.25   $228.30  
  Purchase #5 $210.38   6.709%   $224.4944   $224.49   $224.50   $224.50  
  Purchase #6 $65.98   4.781%   $69.1345   $69.13   $69.15   $69.10  
  Purchase #7 $181.33   7.709%   $195.3087   $195.31   $195.30   $195.30  
  7 purchase totals = $1,058.04       $1,118.5480   $1,118.53   $1,118.50   $1,118.60