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 $55.33   12.361%   $62.1693   $62.17   $62.15   $62.20  
  Purchase #2 $211.57   4.574%   $221.2472   $221.25   $221.25   $221.20  
  Purchase #3 $222.66   4.106%   $231.8024   $231.80   $231.80   $231.80  
  Purchase #4 $165.36   8.526%   $179.4586   $179.46   $179.45   $179.50  
  Purchase #5 $82.81   9.293%   $90.5055   $90.51   $90.50   $90.50  
  Purchase #6 $59.45   6.528%   $63.3309   $63.33   $63.35   $63.30  
  Purchase #7 $8.81   11.341%   $9.8091   $9.81   $9.80   $9.80  
  7 purchase totals = $805.99       $858.3230   $858.33   $858.30   $858.30