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 $122.42   10.226%   $134.9387   $134.94   $134.95   $134.90  
  Purchase #2 $168.61   7.868%   $181.8762   $181.88   $181.90   $181.90  
  Purchase #3 $18.69   7.308%   $20.0559   $20.06   $20.05   $20.10  
  Purchase #4 $32.60   10.657%   $36.0742   $36.07   $36.05   $36.10  
  Purchase #5 $53.46   8.489%   $57.9982   $58.00   $58.00   $58.00  
  Purchase #6 $215.43   9.269%   $235.3982   $235.40   $235.40   $235.40  
  Purchase #7 $250.69   10.353%   $276.6439   $276.64   $276.65   $276.60  
  7 purchase totals = $861.90       $942.9853   $942.99   $943.00   $943.00