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 $84.73   12.514%   $95.3331   $95.33   $95.35   $95.30  
  Purchase #2 $208.77   8.658%   $226.8453   $226.85   $226.85   $226.80  
  Purchase #3 $9.38   9.700%   $10.2899   $10.29   $10.30   $10.30  
  Purchase #4 $247.35   10.836%   $274.1528   $274.15   $274.15   $274.20  
  Purchase #5 $34.32   9.639%   $37.6281   $37.63   $37.65   $37.60  
  Purchase #6 $13.66   5.836%   $14.4572   $14.46   $14.45   $14.50  
  Purchase #7 $74.78   9.376%   $81.7914   $81.79   $81.80   $81.80  
  7 purchase totals = $672.99       $740.4978   $740.50   $740.55   $740.50