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 $144.97   5.631%   $153.1333   $153.13   $153.15   $153.10  
  Purchase #2 $51.28   10.235%   $56.5285   $56.53   $56.55   $56.50  
  Purchase #3 $226.42   8.681%   $246.0755   $246.08   $246.10   $246.10  
  Purchase #4 $246.88   8.140%   $266.976   $266.98   $267.00   $267.00  
  Purchase #5 $121.48   10.242%   $133.922   $133.92   $133.90   $133.90  
  Purchase #6 $43.36   6.849%   $46.3297   $46.33   $46.35   $46.30  
  Purchase #7 $243.78   4.486%   $254.716   $254.72   $254.70   $254.70  
  7 purchase totals = $1,078.17       $1,157.6810   $1,157.69   $1,157.75   $1,157.60