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 $114.46   8.424%   $124.1021   $124.10   $124.10   $124.10  
  Purchase #2 $185.47   3.623%   $192.1896   $192.19   $192.20   $192.20  
  Purchase #3 $20.99   12.626%   $23.6402   $23.64   $23.65   $23.60  
  Purchase #4 $241.27   4.790%   $252.8268   $252.83   $252.85   $252.80  
  Purchase #5 $86.99   6.436%   $92.5887   $92.59   $92.60   $92.60  
  Purchase #6 $186.26   9.266%   $203.5189   $203.52   $203.50   $203.50  
  Purchase #7 $22.49   9.621%   $24.6538   $24.65   $24.65   $24.70  
  7 purchase totals = $857.93       $913.5201   $913.52   $913.55   $913.50