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 $183.54   10.195%   $202.2519   $202.25   $202.25   $202.30  
  Purchase #2 $119.99   13.315%   $135.9667   $135.97   $135.95   $136.00  
  Purchase #3 $114.59   10.450%   $126.5647   $126.56   $126.55   $126.60  
  Purchase #4 $53.96   8.451%   $58.5202   $58.52   $58.50   $58.50  
  Purchase #5 $104.60   4.442%   $109.2463   $109.25   $109.25   $109.20  
  Purchase #6 $94.64   10.758%   $104.8214   $104.82   $104.80   $104.80  
  Purchase #7 $235.27   11.706%   $262.8107   $262.81   $262.80   $262.80  
  7 purchase totals = $906.59       $1,000.1819   $1,000.18   $1,000.10   $1,000.20