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 $177.44   11.568%   $197.9663   $197.97   $197.95   $198.00  
  Purchase #2 $227.30   10.555%   $251.2915   $251.29   $251.30   $251.30  
  Purchase #3 $151.46   5.766%   $160.1932   $160.19   $160.20   $160.20  
  Purchase #4 $221.36   8.789%   $240.8153   $240.82   $240.80   $240.80  
  Purchase #5 $99.70   13.595%   $113.2542   $113.25   $113.25   $113.30  
  Purchase #6 $180.70   10.665%   $199.9717   $199.97   $199.95   $200.00  
  Purchase #7 $34.99   9.305%   $38.2458   $38.25   $38.25   $38.20  
  7 purchase totals = $1,092.95       $1,201.7380   $1,201.74   $1,201.70   $1,201.80