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 $236.51   11.766%   $264.3378   $264.34   $264.35   $264.30  
  Purchase #2 $196.58   5.869%   $208.1173   $208.12   $208.10   $208.10  
  Purchase #3 $191.63   5.326%   $201.8362   $201.84   $201.85   $201.80  
  Purchase #4 $247.80   8.554%   $268.9968   $269.00   $269.00   $269.00  
  Purchase #5 $157.30   6.427%   $167.4097   $167.41   $167.40   $167.40  
  Purchase #6 $129.76   9.697%   $142.3428   $142.34   $142.35   $142.30  
  Purchase #7 $206.43   6.620%   $220.0957   $220.10   $220.10   $220.10  
  7 purchase totals = $1,366.01       $1,473.1363   $1,473.15   $1,473.15   $1,473.00