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 $132.86   13.640%   $150.9821   $150.98   $151.00   $151.00  
  Purchase #2 $89.73   10.201%   $98.8834   $98.88   $98.90   $98.90  
  Purchase #3 $147.47   6.661%   $157.293   $157.29   $157.30   $157.30  
  Purchase #4 $26.26   13.766%   $29.875   $29.88   $29.90   $29.90  
  Purchase #5 $107.27   10.535%   $118.5709   $118.57   $118.55   $118.60  
  Purchase #6 $244.81   3.611%   $253.6501   $253.65   $253.65   $253.70  
  Purchase #7 $227.70   5.683%   $240.6402   $240.64   $240.65   $240.60  
  7 purchase totals = $976.10       $1,049.8947   $1,049.89   $1,049.95   $1,050.00