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 $238.80   12.651%   $269.0106   $269.01   $269.00   $269.00  
  Purchase #2 $66.26   8.695%   $72.0213   $72.02   $72.00   $72.00  
  Purchase #3 $244.77   11.220%   $272.2332   $272.23   $272.25   $272.20  
  Purchase #4 $108.67   6.411%   $115.6368   $115.64   $115.65   $115.60  
  Purchase #5 $178.30   13.278%   $201.9747   $201.97   $201.95   $202.00  
  Purchase #6 $244.89   5.243%   $257.7296   $257.73   $257.75   $257.70  
  Purchase #7 $245.78   5.771%   $259.964   $259.96   $259.95   $260.00  
  7 purchase totals = $1,327.47       $1,448.5702   $1,448.56   $1,448.55   $1,448.50