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 $134.47   13.746%   $152.9542   $152.95   $152.95   $153.00  
  Purchase #2 $27.67   7.242%   $29.6739   $29.67   $29.65   $29.70  
  Purchase #3 $229.45   4.347%   $239.4242   $239.42   $239.40   $239.40  
  Purchase #4 $171.70   8.632%   $186.5211   $186.52   $186.50   $186.50  
  Purchase #5 $244.52   9.491%   $267.7274   $267.73   $267.75   $267.70  
  Purchase #6 $206.62   8.182%   $223.5256   $223.53   $223.55   $223.50  
  Purchase #7 $195.59   7.217%   $209.7057   $209.71   $209.70   $209.70  
  7 purchase totals = $1,210.02       $1,309.5321   $1,309.53   $1,309.50   $1,309.50