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 $244.38   13.401%   $277.1294   $277.13   $277.15   $277.10  
  Purchase #2 $129.94   9.812%   $142.6897   $142.69   $142.70   $142.70  
  Purchase #3 $119.59   7.857%   $128.9862   $128.99   $129.00   $129.00  
  Purchase #4 $47.31   7.817%   $51.0082   $51.01   $51.00   $51.00  
  Purchase #5 $166.30   10.152%   $183.1828   $183.18   $183.20   $183.20  
  Purchase #6 $79.81   9.218%   $87.1669   $87.17   $87.15   $87.20  
  Purchase #7 $190.96   7.851%   $205.9523   $205.95   $205.95   $206.00  
  7 purchase totals = $978.29       $1,076.1155   $1,076.12   $1,076.15   $1,076.20