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 $49.33   13.858%   $56.1662   $56.17   $56.15   $56.20  
  Purchase #2 $90.33   9.403%   $98.8237   $98.82   $98.80   $98.80  
  Purchase #3 $247.54   5.155%   $260.3007   $260.30   $260.30   $260.30  
  Purchase #4 $79.45   13.178%   $89.9199   $89.92   $89.90   $89.90  
  Purchase #5 $210.67   13.651%   $239.4286   $239.43   $239.45   $239.40  
  Purchase #6 $112.37   7.336%   $120.6135   $120.61   $120.60   $120.60  
  Purchase #7 $128.39   9.574%   $140.6821   $140.68   $140.70   $140.70  
  7 purchase totals = $918.08       $1,005.9347   $1,005.93   $1,005.90   $1,005.90