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 $95.57   10.601%   $105.7014   $105.70   $105.70   $105.70  
  Purchase #2 $227.46   7.672%   $244.9107   $244.91   $244.90   $244.90  
  Purchase #3 $174.31   4.365%   $181.9186   $181.92   $181.90   $181.90  
  Purchase #4 $54.97   4.748%   $57.58   $57.58   $57.60   $57.60  
  Purchase #5 $114.43   6.195%   $121.5189   $121.52   $121.50   $121.50  
  Purchase #6 $134.62   9.246%   $147.067   $147.07   $147.05   $147.10  
  Purchase #7 $115.25   9.348%   $126.0236   $126.02   $126.00   $126.00  
  7 purchase totals = $916.61       $984.7202   $984.72   $984.65   $984.70