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 $79.70   5.834%   $84.3497   $84.35   $84.35   $84.30  
  Purchase #2 $208.26   12.192%   $233.6511   $233.65   $233.65   $233.70  
  Purchase #3 $160.76   9.503%   $176.037   $176.04   $176.05   $176.00  
  Purchase #4 $91.58   12.566%   $103.0879   $103.09   $103.10   $103.10  
  Purchase #5 $165.64   9.349%   $181.1257   $181.13   $181.15   $181.10  
  Purchase #6 $70.44   3.436%   $72.8603   $72.86   $72.85   $72.90  
  Purchase #7 $135.35   6.322%   $143.9068   $143.91   $143.90   $143.90  
  7 purchase totals = $911.73       $995.0185   $995.03   $995.05   $995.00