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 $168.52   10.821%   $186.7555   $186.76   $186.75   $186.80  
  Purchase #2 $70.63   11.837%   $78.9905   $78.99   $79.00   $79.00  
  Purchase #3 $73.49   4.216%   $76.5883   $76.59   $76.60   $76.60  
  Purchase #4 $185.48   10.377%   $204.7273   $204.73   $204.75   $204.70  
  Purchase #5 $242.43   12.446%   $272.6028   $272.60   $272.60   $272.60  
  Purchase #6 $54.70   3.412%   $56.5664   $56.57   $56.55   $56.60  
  Purchase #7 $152.58   11.236%   $169.7239   $169.72   $169.70   $169.70  
  7 purchase totals = $947.83       $1,045.9547   $1,045.96   $1,045.95   $1,046.00