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 $95.47   6.779%   $101.9419   $101.94   $101.95   $101.90  
  Purchase #2 $240.80   10.762%   $266.7149   $266.71   $266.70   $266.70  
  Purchase #3 $193.74   6.304%   $205.9534   $205.95   $205.95   $206.00  
  Purchase #4 $13.64   10.653%   $15.0931   $15.09   $15.10   $15.10  
  Purchase #5 $120.77   11.490%   $134.6465   $134.65   $134.65   $134.60  
  Purchase #6 $199.93   6.169%   $212.2637   $212.26   $212.25   $212.30  
  Purchase #7 $125.63   8.122%   $135.8337   $135.83   $135.85   $135.80  
  7 purchase totals = $989.98       $1,072.4472   $1,072.43   $1,072.45   $1,072.40