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 $176.54   7.649%   $190.0435   $190.04   $190.05   $190.00  
  Purchase #2 $12.38   7.451%   $13.3024   $13.30   $13.30   $13.30  
  Purchase #3 $68.92   7.141%   $73.8416   $73.84   $73.85   $73.80  
  Purchase #4 $83.93   8.187%   $90.8013   $90.80   $90.80   $90.80  
  Purchase #5 $108.59   9.501%   $118.9071   $118.91   $118.90   $118.90  
  Purchase #6 $46.79   12.156%   $52.4778   $52.48   $52.50   $52.50  
  Purchase #7 $136.96   5.496%   $144.4873   $144.49   $144.50   $144.50  
  7 purchase totals = $634.11       $683.8610   $683.86   $683.90   $683.80