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 $232.92   6.759%   $248.6631   $248.66   $248.65   $248.70  
  Purchase #2 $216.37   13.674%   $245.9564   $245.96   $245.95   $246.00  
  Purchase #3 $125.69   12.314%   $141.1675   $141.17   $141.15   $141.20  
  Purchase #4 $60.77   10.202%   $66.9698   $66.97   $66.95   $67.00  
  Purchase #5 $63.80   3.160%   $65.8161   $65.82   $65.80   $65.80  
  Purchase #6 $162.36   8.657%   $176.4155   $176.42   $176.40   $176.40  
  Purchase #7 $79.39   9.561%   $86.9805   $86.98   $87.00   $87.00  
  7 purchase totals = $941.30       $1,031.9689   $1,031.98   $1,031.90   $1,032.10