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 $195.49   7.243%   $209.6493   $209.65   $209.65   $209.60  
  Purchase #2 $82.30   6.674%   $87.7927   $87.79   $87.80   $87.80  
  Purchase #3 $24.45   9.450%   $26.7605   $26.76   $26.75   $26.80  
  Purchase #4 $226.56   12.514%   $254.9117   $254.91   $254.90   $254.90  
  Purchase #5 $183.45   13.553%   $208.313   $208.31   $208.30   $208.30  
  Purchase #6 $14.86   9.527%   $16.2757   $16.28   $16.30   $16.30  
  Purchase #7 $239.29   8.648%   $259.9838   $259.98   $260.00   $260.00  
  7 purchase totals = $966.40       $1,063.6867   $1,063.68   $1,063.70   $1,063.70