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 $232.28   10.806%   $257.3802   $257.38   $257.40   $257.40  
  Purchase #2 $165.90   6.131%   $176.0713   $176.07   $176.05   $176.10  
  Purchase #3 $216.38   8.707%   $235.2202   $235.22   $235.20   $235.20  
  Purchase #4 $167.94   11.172%   $186.7023   $186.70   $186.70   $186.70  
  Purchase #5 $198.98   13.383%   $225.6095   $225.61   $225.60   $225.60  
  Purchase #6 $111.83   5.658%   $118.1573   $118.16   $118.15   $118.20  
  Purchase #7 $238.29   10.163%   $262.5074   $262.51   $262.50   $262.50  
  7 purchase totals = $1,331.60       $1,461.6482   $1,461.65   $1,461.60   $1,461.70