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 $61.61   3.516%   $63.7762   $63.78   $63.80   $63.80  
  Purchase #2 $211.74   3.668%   $219.5066   $219.51   $219.50   $219.50  
  Purchase #3 $220.70   13.202%   $249.8368   $249.84   $249.85   $249.80  
  Purchase #4 $111.52   12.675%   $125.6552   $125.66   $125.65   $125.70  
  Purchase #5 $224.43   7.603%   $241.4934   $241.49   $241.50   $241.50  
  Purchase #6 $23.63   12.116%   $26.493   $26.49   $26.50   $26.50  
  Purchase #7 $167.36   3.340%   $172.9498   $172.95   $172.95   $172.90  
  7 purchase totals = $1,020.99       $1,099.7110   $1,099.72   $1,099.75   $1,099.70