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 $93.46   6.564%   $99.5947   $99.59   $99.60   $99.60  
  Purchase #2 $246.37   3.408%   $254.7663   $254.77   $254.75   $254.80  
  Purchase #3 $58.76   6.617%   $62.6481   $62.65   $62.65   $62.60  
  Purchase #4 $199.62   3.826%   $207.2575   $207.26   $207.25   $207.30  
  Purchase #5 $37.71   10.559%   $41.6918   $41.69   $41.70   $41.70  
  Purchase #6 $187.61   8.812%   $204.1422   $204.14   $204.15   $204.10  
  Purchase #7 $134.74   3.270%   $139.146   $139.15   $139.15   $139.10  
  7 purchase totals = $958.27       $1,009.2466   $1,009.25   $1,009.25   $1,009.20