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 $240.27   11.616%   $268.1798   $268.18   $268.20   $268.20  
  Purchase #2 $154.33   5.808%   $163.2935   $163.29   $163.30   $163.30  
  Purchase #3 $167.55   12.209%   $188.0062   $188.01   $188.00   $188.00  
  Purchase #4 $168.82   3.453%   $174.6494   $174.65   $174.65   $174.60  
  Purchase #5 $99.89   11.437%   $111.3144   $111.31   $111.30   $111.30  
  Purchase #6 $88.33   3.463%   $91.3889   $91.39   $91.40   $91.40  
  Purchase #7 $8.61   5.335%   $9.0693   $9.07   $9.05   $9.10  
  7 purchase totals = $927.80       $1,005.9015   $1,005.90   $1,005.90   $1,005.90