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 $239.39   12.359%   $268.9762   $268.98   $269.00   $269.00  
  Purchase #2 $247.50   4.257%   $258.0361   $258.04   $258.05   $258.00  
  Purchase #3 $36.37   4.283%   $37.9277   $37.93   $37.95   $37.90  
  Purchase #4 $230.41   9.128%   $251.4418   $251.44   $251.45   $251.40  
  Purchase #5 $216.48   13.375%   $245.4342   $245.43   $245.45   $245.40  
  Purchase #6 $191.84   9.724%   $210.4945   $210.49   $210.50   $210.50  
  Purchase #7 $229.52   5.475%   $242.0862   $242.09   $242.10   $242.10  
  7 purchase totals = $1,391.51       $1,514.3967   $1,514.40   $1,514.50   $1,514.30