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 $38.84   13.521%   $44.0916   $44.09   $44.10   $44.10  
  Purchase #2 $226.84   8.496%   $246.1123   $246.11   $246.10   $246.10  
  Purchase #3 $155.42   11.786%   $173.7378   $173.74   $173.75   $173.70  
  Purchase #4 $185.28   6.802%   $197.8827   $197.88   $197.90   $197.90  
  Purchase #5 $94.97   11.326%   $105.7263   $105.73   $105.75   $105.70  
  Purchase #6 $106.71   12.863%   $120.4361   $120.44   $120.45   $120.40  
  Purchase #7 $158.91   9.550%   $174.0859   $174.09   $174.10   $174.10  
  7 purchase totals = $966.97       $1,062.0727   $1,062.08   $1,062.15   $1,062.00