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 $86.96   11.293%   $96.7804   $96.78   $96.80   $96.80  
  Purchase #2 $115.69   8.714%   $125.7712   $125.77   $125.75   $125.80  
  Purchase #3 $109.98   6.359%   $116.9736   $116.97   $116.95   $117.00  
  Purchase #4 $212.77   10.455%   $235.0151   $235.02   $235.00   $235.00  
  Purchase #5 $153.38   6.282%   $163.0153   $163.02   $163.00   $163.00  
  Purchase #6 $221.47   4.750%   $231.9898   $231.99   $232.00   $232.00  
  Purchase #7 $30.99   6.773%   $33.089   $33.09   $33.10   $33.10  
  7 purchase totals = $931.24       $1,002.6344   $1,002.64   $1,002.60   $1,002.70