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 $211.75   10.758%   $234.5301   $234.53   $234.55   $234.50  
  Purchase #2 $55.59   3.131%   $57.3305   $57.33   $57.35   $57.30  
  Purchase #3 $248.49   3.326%   $256.7548   $256.75   $256.75   $256.80  
  Purchase #4 $118.99   6.115%   $126.2662   $126.27   $126.25   $126.30  
  Purchase #5 $164.25   8.157%   $177.6479   $177.65   $177.65   $177.60  
  Purchase #6 $13.30   6.125%   $14.1146   $14.11   $14.10   $14.10  
  Purchase #7 $154.25   10.220%   $170.0144   $170.01   $170.00   $170.00  
  7 purchase totals = $966.62       $1,036.6585   $1,036.65   $1,036.65   $1,036.60