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 $65.83   11.723%   $73.5473   $73.55   $73.55   $73.50  
  Purchase #2 $231.38   10.744%   $256.2395   $256.24   $256.25   $256.20  
  Purchase #3 $124.67   13.166%   $141.0841   $141.08   $141.10   $141.10  
  Purchase #4 $62.85   9.123%   $68.5838   $68.58   $68.60   $68.60  
  Purchase #5 $159.91   7.761%   $172.3206   $172.32   $172.30   $172.30  
  Purchase #6 $47.84   7.807%   $51.5749   $51.57   $51.55   $51.60  
  Purchase #7 $12.72   5.389%   $13.4055   $13.41   $13.40   $13.40  
  7 purchase totals = $705.20       $776.7557   $776.75   $776.75   $776.70