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 $228.82   11.338%   $254.7636   $254.76   $254.75   $254.80  
  Purchase #2 $49.29   10.625%   $54.5271   $54.53   $54.55   $54.50  
  Purchase #3 $162.78   9.193%   $177.7444   $177.74   $177.75   $177.70  
  Purchase #4 $87.75   11.203%   $97.5806   $97.58   $97.60   $97.60  
  Purchase #5 $72.79   13.415%   $82.5548   $82.55   $82.55   $82.60  
  Purchase #6 $198.86   4.140%   $207.0928   $207.09   $207.10   $207.10  
  Purchase #7 $53.80   5.311%   $56.6573   $56.66   $56.65   $56.70  
  7 purchase totals = $854.09       $930.9206   $930.91   $930.95   $931.00