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 $88.46   9.429%   $96.8009   $96.80   $96.80   $96.80  
  Purchase #2 $244.27   13.181%   $276.4672   $276.47   $276.45   $276.50  
  Purchase #3 $218.60   3.801%   $226.909   $226.91   $226.90   $226.90  
  Purchase #4 $219.51   10.481%   $242.5168   $242.52   $242.50   $242.50  
  Purchase #5 $19.87   11.290%   $22.1133   $22.11   $22.10   $22.10  
  Purchase #6 $78.30   10.602%   $86.6014   $86.60   $86.60   $86.60  
  Purchase #7 $230.93   5.145%   $242.8113   $242.81   $242.80   $242.80  
  7 purchase totals = $1,099.94       $1,194.2199   $1,194.22   $1,194.15   $1,194.20