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 $57.58   7.626%   $61.9711   $61.97   $61.95   $62.00  
  Purchase #2 $159.50   13.582%   $181.1633   $181.16   $181.15   $181.20  
  Purchase #3 $230.86   6.713%   $246.3576   $246.36   $246.35   $246.40  
  Purchase #4 $164.89   9.164%   $180.0005   $180.00   $180.00   $180.00  
  Purchase #5 $45.85   13.570%   $52.0718   $52.07   $52.05   $52.10  
  Purchase #6 $18.81   12.331%   $21.1295   $21.13   $21.15   $21.10  
  Purchase #7 $106.38   13.350%   $120.5817   $120.58   $120.60   $120.60  
  7 purchase totals = $783.87       $863.2755   $863.27   $863.25   $863.40