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 $151.82   13.270%   $171.9665   $171.97   $171.95   $172.00  
  Purchase #2 $50.93   6.270%   $54.1233   $54.12   $54.10   $54.10  
  Purchase #3 $233.77   6.165%   $248.1819   $248.18   $248.20   $248.20  
  Purchase #4 $129.41   6.544%   $137.8786   $137.88   $137.90   $137.90  
  Purchase #5 $106.94   12.113%   $119.8936   $119.89   $119.90   $119.90  
  Purchase #6 $139.41   13.496%   $158.2248   $158.22   $158.20   $158.20  
  Purchase #7 $162.44   4.299%   $169.4233   $169.42   $169.40   $169.40  
  7 purchase totals = $974.72       $1,059.6920   $1,059.68   $1,059.65   $1,059.70