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 $62.64   7.363%   $67.2522   $67.25   $67.25   $67.30  
  Purchase #2 $156.33   12.604%   $176.0338   $176.03   $176.05   $176.00  
  Purchase #3 $72.98   12.755%   $82.2886   $82.29   $82.30   $82.30  
  Purchase #4 $43.69   4.850%   $45.809   $45.81   $45.80   $45.80  
  Purchase #5 $248.97   6.456%   $265.0435   $265.04   $265.05   $265.00  
  Purchase #6 $40.55   8.651%   $44.058   $44.06   $44.05   $44.10  
  Purchase #7 $26.74   12.803%   $30.1635   $30.16   $30.15   $30.20  
  7 purchase totals = $651.90       $710.6486   $710.64   $710.65   $710.70