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 $160.55   10.668%   $177.6775   $177.68   $177.70   $177.70  
  Purchase #2 $247.42   11.254%   $275.2646   $275.26   $275.25   $275.30  
  Purchase #3 $117.82   8.239%   $127.5272   $127.53   $127.55   $127.50  
  Purchase #4 $19.64   10.551%   $21.7122   $21.71   $21.70   $21.70  
  Purchase #5 $186.92   3.311%   $193.1089   $193.11   $193.10   $193.10  
  Purchase #6 $111.53   13.330%   $126.3969   $126.40   $126.40   $126.40  
  Purchase #7 $113.52   8.464%   $123.1283   $123.13   $123.15   $123.10  
  7 purchase totals = $957.40       $1,044.8156   $1,044.82   $1,044.85   $1,044.80