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 $67.40   3.373%   $69.6734   $69.67   $69.65   $69.70  
  Purchase #2 $250.95   9.769%   $275.4653   $275.47   $275.45   $275.50  
  Purchase #3 $121.35   6.381%   $129.0933   $129.09   $129.10   $129.10  
  Purchase #4 $111.57   11.839%   $124.7788   $124.78   $124.80   $124.80  
  Purchase #5 $100.87   4.452%   $105.3607   $105.36   $105.35   $105.40  
  Purchase #6 $244.95   7.153%   $262.4713   $262.47   $262.45   $262.50  
  Purchase #7 $83.80   3.107%   $86.4037   $86.40   $86.40   $86.40  
  7 purchase totals = $980.89       $1,053.2465   $1,053.24   $1,053.20   $1,053.40