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 $159.73   10.186%   $176.0001   $176.00   $176.00   $176.00  
  Purchase #2 $55.86   10.687%   $61.8298   $61.83   $61.85   $61.80  
  Purchase #3 $105.38   10.257%   $116.1888   $116.19   $116.20   $116.20  
  Purchase #4 $186.73   4.707%   $195.5194   $195.52   $195.50   $195.50  
  Purchase #5 $230.87   12.159%   $258.9415   $258.94   $258.95   $258.90  
  Purchase #6 $47.46   3.280%   $49.0167   $49.02   $49.00   $49.00  
  Purchase #7 $91.96   3.650%   $95.3165   $95.32   $95.30   $95.30  
  7 purchase totals = $877.99       $952.8128   $952.82   $952.80   $952.70