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 $51.72   10.844%   $57.3285   $57.33   $57.35   $57.30  
  Purchase #2 $126.65   5.832%   $134.0362   $134.04   $134.05   $134.00  
  Purchase #3 $213.92   11.108%   $237.6822   $237.68   $237.70   $237.70  
  Purchase #4 $52.31   7.509%   $56.238   $56.24   $56.25   $56.20  
  Purchase #5 $247.46   6.769%   $264.2106   $264.21   $264.20   $264.20  
  Purchase #6 $68.87   5.534%   $72.6813   $72.68   $72.70   $72.70  
  Purchase #7 $153.87   12.417%   $172.976   $172.98   $173.00   $173.00  
  7 purchase totals = $914.80       $995.1528   $995.16   $995.25   $995.10