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 $48.81   6.533%   $51.9988   $52.00   $52.00   $52.00  
  Purchase #2 $5.47   9.778%   $6.0049   $6.00   $6.00   $6.00  
  Purchase #3 $220.34   11.289%   $245.2142   $245.21   $245.20   $245.20  
  Purchase #4 $88.48   5.778%   $93.5924   $93.59   $93.60   $93.60  
  Purchase #5 $225.66   3.826%   $234.2938   $234.29   $234.30   $234.30  
  Purchase #6 $87.90   9.338%   $96.1081   $96.11   $96.10   $96.10  
  Purchase #7 $127.80   12.111%   $143.2779   $143.28   $143.30   $143.30  
  7 purchase totals = $804.46       $870.4901   $870.48   $870.50   $870.50