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 $96.69   13.362%   $109.6097   $109.61   $109.60   $109.60  
  Purchase #2 $178.50   11.867%   $199.6826   $199.68   $199.70   $199.70  
  Purchase #3 $11.52   3.517%   $11.9252   $11.93   $11.95   $11.90  
  Purchase #4 $230.54   11.625%   $257.3403   $257.34   $257.35   $257.30  
  Purchase #5 $238.69   12.153%   $267.698   $267.70   $267.70   $267.70  
  Purchase #6 $171.46   11.719%   $191.5534   $191.55   $191.55   $191.60  
  Purchase #7 $81.43   13.755%   $92.6307   $92.63   $92.65   $92.60  
  7 purchase totals = $1,008.83       $1,130.4399   $1,130.44   $1,130.50   $1,130.40