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 $124.52   4.671%   $130.3363   $130.34   $130.35   $130.30  
  Purchase #2 $83.94   13.645%   $95.3936   $95.39   $95.40   $95.40  
  Purchase #3 $147.65   3.220%   $152.4043   $152.40   $152.40   $152.40  
  Purchase #4 $60.97   13.658%   $69.2973   $69.30   $69.30   $69.30  
  Purchase #5 $180.83   9.803%   $198.5568   $198.56   $198.55   $198.60  
  Purchase #6 $207.28   6.470%   $220.691   $220.69   $220.70   $220.70  
  Purchase #7 $23.52   13.177%   $26.6192   $26.62   $26.60   $26.60  
  7 purchase totals = $828.71       $893.2985   $893.30   $893.30   $893.30