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 $54.96   11.371%   $61.2095   $61.21   $61.20   $61.20  
  Purchase #2 $217.79   4.357%   $227.2791   $227.28   $227.30   $227.30  
  Purchase #3 $37.79   10.622%   $41.8041   $41.80   $41.80   $41.80  
  Purchase #4 $93.38   3.193%   $96.3616   $96.36   $96.35   $96.40  
  Purchase #5 $65.92   8.726%   $71.6722   $71.67   $71.65   $71.70  
  Purchase #6 $54.34   4.850%   $56.9755   $56.98   $57.00   $57.00  
  Purchase #7 $71.69   10.209%   $79.0088   $79.01   $79.00   $79.00  
  7 purchase totals = $595.87       $634.3108   $634.31   $634.30   $634.40