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 $215.79   7.796%   $232.613   $232.61   $232.60   $232.60  
  Purchase #2 $31.95   10.792%   $35.398   $35.40   $35.40   $35.40  
  Purchase #3 $43.83   13.779%   $49.8693   $49.87   $49.85   $49.90  
  Purchase #4 $109.48   3.823%   $113.6654   $113.67   $113.65   $113.70  
  Purchase #5 $243.26   6.252%   $258.4686   $258.47   $258.45   $258.50  
  Purchase #6 $106.56   13.866%   $121.3356   $121.34   $121.35   $121.30  
  Purchase #7 $177.27   4.533%   $185.3056   $185.31   $185.30   $185.30  
  7 purchase totals = $928.14       $996.6555   $996.67   $996.60   $996.70