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 $207.48   10.733%   $229.7488   $229.75   $229.75   $229.70  
  Purchase #2 $108.39   11.508%   $120.8635   $120.86   $120.85   $120.90  
  Purchase #3 $5.28   11.859%   $5.9062   $5.91   $5.90   $5.90  
  Purchase #4 $105.57   5.703%   $111.5907   $111.59   $111.60   $111.60  
  Purchase #5 $216.51   6.821%   $231.2781   $231.28   $231.30   $231.30  
  Purchase #6 $51.45   10.715%   $56.9629   $56.96   $56.95   $57.00  
  Purchase #7 $200.66   13.729%   $228.2086   $228.21   $228.20   $228.20  
  7 purchase totals = $895.34       $984.5588   $984.56   $984.55   $984.60