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 $180.52   13.558%   $204.9949   $204.99   $205.00   $205.00  
  Purchase #2 $229.86   13.695%   $261.3393   $261.34   $261.35   $261.30  
  Purchase #3 $41.68   7.462%   $44.7902   $44.79   $44.80   $44.80  
  Purchase #4 $117.70   4.337%   $122.8046   $122.80   $122.80   $122.80  
  Purchase #5 $41.64   6.436%   $44.32   $44.32   $44.30   $44.30  
  Purchase #6 $221.44   4.362%   $231.0992   $231.10   $231.10   $231.10  
  Purchase #7 $168.84   5.422%   $177.9945   $177.99   $178.00   $178.00  
  7 purchase totals = $1,001.68       $1,087.3427   $1,087.33   $1,087.35   $1,087.30