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 $216.67   4.792%   $227.0528   $227.05   $227.05   $227.10  
  Purchase #2 $121.70   3.776%   $126.2954   $126.30   $126.30   $126.30  
  Purchase #3 $37.95   5.628%   $40.0858   $40.09   $40.10   $40.10  
  Purchase #4 $203.36   12.855%   $229.5019   $229.50   $229.50   $229.50  
  Purchase #5 $212.29   10.566%   $234.7206   $234.72   $234.70   $234.70  
  Purchase #6 $24.54   5.296%   $25.8396   $25.84   $25.85   $25.80  
  Purchase #7 $99.81   11.518%   $111.3061   $111.31   $111.30   $111.30  
  7 purchase totals = $916.32       $994.8022   $994.81   $994.80   $994.80