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 $53.44   11.371%   $59.5167   $59.52   $59.50   $59.50  
  Purchase #2 $195.54   11.260%   $217.5578   $217.56   $217.55   $217.60  
  Purchase #3 $185.36   9.513%   $202.9933   $202.99   $203.00   $203.00  
  Purchase #4 $171.57   8.322%   $185.8481   $185.85   $185.85   $185.80  
  Purchase #5 $19.63   6.804%   $20.9656   $20.97   $20.95   $21.00  
  Purchase #6 $175.93   7.210%   $188.6146   $188.61   $188.60   $188.60  
  Purchase #7 $120.30   10.556%   $132.9989   $133.00   $133.00   $133.00  
  7 purchase totals = $921.77       $1,008.4950   $1,008.50   $1,008.45   $1,008.50