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 $119.85   12.240%   $134.5196   $134.52   $134.50   $134.50  
  Purchase #2 $78.53   4.870%   $82.3544   $82.35   $82.35   $82.40  
  Purchase #3 $106.48   9.461%   $116.5541   $116.55   $116.55   $116.60  
  Purchase #4 $206.43   10.368%   $227.8327   $227.83   $227.85   $227.80  
  Purchase #5 $159.39   10.835%   $176.6599   $176.66   $176.65   $176.70  
  Purchase #6 $224.66   10.641%   $248.5661   $248.57   $248.55   $248.60  
  Purchase #7 $20.65   8.263%   $22.3563   $22.36   $22.35   $22.40  
  7 purchase totals = $915.99       $1,008.8431   $1,008.84   $1,008.80   $1,009.00