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 $47.67   9.521%   $52.2087   $52.21   $52.20   $52.20  
  Purchase #2 $119.74   8.308%   $129.688   $129.69   $129.70   $129.70  
  Purchase #3 $90.25   10.298%   $99.5439   $99.54   $99.55   $99.50  
  Purchase #4 $240.30   6.423%   $255.7345   $255.73   $255.75   $255.70  
  Purchase #5 $155.66   11.561%   $173.6559   $173.66   $173.65   $173.70  
  Purchase #6 $46.83   12.381%   $52.628   $52.63   $52.65   $52.60  
  Purchase #7 $181.33   12.555%   $204.096   $204.10   $204.10   $204.10  
  7 purchase totals = $881.78       $967.5550   $967.56   $967.60   $967.50