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 $208.47   7.506%   $224.1178   $224.12   $224.10   $224.10  
  Purchase #2 $221.72   12.223%   $248.8208   $248.82   $248.80   $248.80  
  Purchase #3 $49.88   10.322%   $55.0286   $55.03   $55.05   $55.00  
  Purchase #4 $195.77   3.523%   $202.667   $202.67   $202.65   $202.70  
  Purchase #5 $124.77   7.836%   $134.547   $134.55   $134.55   $134.50  
  Purchase #6 $120.72   13.156%   $136.6019   $136.60   $136.60   $136.60  
  Purchase #7 $105.88   7.171%   $113.4727   $113.47   $113.45   $113.50  
  7 purchase totals = $1,027.21       $1,115.2558   $1,115.26   $1,115.20   $1,115.20