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 $136.96   11.675%   $152.9501   $152.95   $152.95   $153.00  
  Purchase #2 $132.98   7.527%   $142.9894   $142.99   $143.00   $143.00  
  Purchase #3 $8.73   3.575%   $9.0421   $9.04   $9.05   $9.00  
  Purchase #4 $32.52   12.291%   $36.517   $36.52   $36.50   $36.50  
  Purchase #5 $211.29   12.284%   $237.2449   $237.24   $237.25   $237.20  
  Purchase #6 $165.26   12.737%   $186.3092   $186.31   $186.30   $186.30  
  Purchase #7 $180.67   6.557%   $192.5165   $192.52   $192.50   $192.50  
  7 purchase totals = $868.41       $957.5692   $957.57   $957.55   $957.50