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 $88.50   7.221%   $94.8906   $94.89   $94.90   $94.90  
  Purchase #2 $44.54   13.307%   $50.4669   $50.47   $50.45   $50.50  
  Purchase #3 $77.63   5.255%   $81.7095   $81.71   $81.70   $81.70  
  Purchase #4 $245.52   12.376%   $275.9056   $275.91   $275.90   $275.90  
  Purchase #5 $52.52   5.821%   $55.5772   $55.58   $55.60   $55.60  
  Purchase #6 $127.38   13.227%   $144.2286   $144.23   $144.25   $144.20  
  Purchase #7 $235.42   12.231%   $264.2142   $264.21   $264.20   $264.20  
  7 purchase totals = $871.51       $966.9926   $967.00   $967.00   $967.00