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 $182.30   12.341%   $204.7976   $204.80   $204.80   $204.80  
  Purchase #2 $55.79   6.409%   $59.3656   $59.37   $59.35   $59.40  
  Purchase #3 $187.32   11.818%   $209.4575   $209.46   $209.45   $209.50  
  Purchase #4 $60.28   13.403%   $68.3593   $68.36   $68.35   $68.40  
  Purchase #5 $216.68   3.666%   $224.6235   $224.62   $224.60   $224.60  
  Purchase #6 $248.92   12.524%   $280.0947   $280.09   $280.10   $280.10  
  Purchase #7 $14.98   10.510%   $16.5544   $16.55   $16.55   $16.60  
  7 purchase totals = $966.27       $1,063.2526   $1,063.25   $1,063.20   $1,063.40