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 $32.29   5.755%   $34.1483   $34.15   $34.15   $34.10  
  Purchase #2 $231.41   13.417%   $262.4583   $262.46   $262.45   $262.50  
  Purchase #3 $200.66   11.691%   $224.1192   $224.12   $224.10   $224.10  
  Purchase #4 $241.99   10.262%   $266.823   $266.82   $266.80   $266.80  
  Purchase #5 $45.34   12.354%   $50.9413   $50.94   $50.95   $50.90  
  Purchase #6 $215.82   9.820%   $237.0135   $237.01   $237.00   $237.00  
  Purchase #7 $242.96   5.381%   $256.0337   $256.03   $256.05   $256.00  
  7 purchase totals = $1,210.47       $1,331.5373   $1,331.53   $1,331.50   $1,331.40