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 $60.52   3.378%   $62.5644   $62.56   $62.55   $62.60  
  Purchase #2 $188.62   11.219%   $209.7813   $209.78   $209.80   $209.80  
  Purchase #3 $185.45   10.366%   $204.6737   $204.67   $204.65   $204.70  
  Purchase #4 $134.72   12.138%   $151.0723   $151.07   $151.05   $151.10  
  Purchase #5 $24.30   9.720%   $26.662   $26.66   $26.65   $26.70  
  Purchase #6 $53.26   6.111%   $56.5147   $56.51   $56.50   $56.50  
  Purchase #7 $113.56   4.479%   $118.6464   $118.65   $118.65   $118.60  
  7 purchase totals = $760.43       $829.9148   $829.90   $829.85   $830.00