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 $169.94   6.375%   $180.7737   $180.77   $180.75   $180.80  
  Purchase #2 $39.89   10.500%   $44.0785   $44.08   $44.10   $44.10  
  Purchase #3 $39.35   13.446%   $44.641   $44.64   $44.65   $44.60  
  Purchase #4 $172.44   8.180%   $186.5456   $186.55   $186.55   $186.50  
  Purchase #5 $84.91   6.419%   $90.3604   $90.36   $90.35   $90.40  
  Purchase #6 $70.54   4.558%   $73.7552   $73.76   $73.75   $73.80  
  Purchase #7 $28.41   10.177%   $31.3013   $31.30   $31.30   $31.30  
  7 purchase totals = $605.48       $651.4557   $651.46   $651.45   $651.50