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 $204.98   10.580%   $226.6669   $226.67   $226.65   $226.70  
  Purchase #2 $241.56   11.205%   $268.6268   $268.63   $268.65   $268.60  
  Purchase #3 $98.86   13.154%   $111.864   $111.86   $111.85   $111.90  
  Purchase #4 $212.75   11.815%   $237.8864   $237.89   $237.90   $237.90  
  Purchase #5 $175.49   3.805%   $182.1674   $182.17   $182.15   $182.20  
  Purchase #6 $149.93   12.102%   $168.0745   $168.07   $168.05   $168.10  
  Purchase #7 $61.49   11.808%   $68.7507   $68.75   $68.75   $68.80  
  7 purchase totals = $1,145.06       $1,264.0367   $1,264.04   $1,264.00   $1,264.20