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 $235.87   13.274%   $267.1794   $267.18   $267.20   $267.20  
  Purchase #2 $203.99   3.191%   $210.4993   $210.50   $210.50   $210.50  
  Purchase #3 $136.61   6.835%   $145.9473   $145.95   $145.95   $145.90  
  Purchase #4 $167.26   6.391%   $177.9496   $177.95   $177.95   $177.90  
  Purchase #5 $32.75   7.426%   $35.182   $35.18   $35.20   $35.20  
  Purchase #6 $87.68   7.779%   $94.5006   $94.50   $94.50   $94.50  
  Purchase #7 $107.92   11.653%   $120.4959   $120.50   $120.50   $120.50  
  7 purchase totals = $972.08       $1,051.7541   $1,051.76   $1,051.80   $1,051.70