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 $178.84   13.248%   $202.5327   $202.53   $202.55   $202.50  
  Purchase #2 $42.44   12.362%   $47.6864   $47.69   $47.70   $47.70  
  Purchase #3 $73.82   7.307%   $79.214   $79.21   $79.20   $79.20  
  Purchase #4 $209.46   5.167%   $220.2828   $220.28   $220.30   $220.30  
  Purchase #5 $55.65   9.593%   $60.9885   $60.99   $61.00   $61.00  
  Purchase #6 $238.30   4.436%   $248.871   $248.87   $248.85   $248.90  
  Purchase #7 $118.30   5.606%   $124.9319   $124.93   $124.95   $124.90  
  7 purchase totals = $916.81       $984.5073   $984.50   $984.55   $984.50