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 $63.41   8.744%   $68.9546   $68.95   $68.95   $69.00  
  Purchase #2 $193.90   4.773%   $203.1548   $203.15   $203.15   $203.20  
  Purchase #3 $141.36   13.737%   $160.7786   $160.78   $160.80   $160.80  
  Purchase #4 $176.43   8.376%   $191.2078   $191.21   $191.20   $191.20  
  Purchase #5 $173.87   10.542%   $192.1994   $192.20   $192.20   $192.20  
  Purchase #6 $237.29   11.528%   $264.6448   $264.64   $264.65   $264.60  
  Purchase #7 $76.48   10.328%   $84.3789   $84.38   $84.40   $84.40  
  7 purchase totals = $1,062.74       $1,165.3189   $1,165.31   $1,165.35   $1,165.40