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 $68.58   8.646%   $74.5094   $74.51   $74.50   $74.50  
  Purchase #2 $234.87   11.548%   $261.9928   $261.99   $262.00   $262.00  
  Purchase #3 $148.90   12.144%   $166.9824   $166.98   $167.00   $167.00  
  Purchase #4 $172.80   11.257%   $192.2521   $192.25   $192.25   $192.30  
  Purchase #5 $160.43   7.187%   $171.9601   $171.96   $171.95   $172.00  
  Purchase #6 $93.80   9.593%   $102.7982   $102.80   $102.80   $102.80  
  Purchase #7 $108.48   8.481%   $117.6802   $117.68   $117.70   $117.70  
  7 purchase totals = $987.86       $1,088.1752   $1,088.17   $1,088.20   $1,088.30