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 $181.47   6.471%   $193.2129   $193.21   $193.20   $193.20  
  Purchase #2 $191.46   4.329%   $199.7483   $199.75   $199.75   $199.70  
  Purchase #3 $224.69   3.683%   $232.9653   $232.97   $232.95   $233.00  
  Purchase #4 $81.68   9.486%   $89.4282   $89.43   $89.45   $89.40  
  Purchase #5 $134.86   11.793%   $150.764   $150.76   $150.75   $150.80  
  Purchase #6 $199.26   10.670%   $220.521   $220.52   $220.50   $220.50  
  Purchase #7 $189.71   3.799%   $196.9171   $196.92   $196.90   $196.90  
  7 purchase totals = $1,203.13       $1,283.5568   $1,283.56   $1,283.50   $1,283.50