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 $248.37   6.129%   $263.5926   $263.59   $263.60   $263.60  
  Purchase #2 $245.86   8.419%   $266.559   $266.56   $266.55   $266.60  
  Purchase #3 $56.59   11.163%   $62.9071   $62.91   $62.90   $62.90  
  Purchase #4 $219.35   9.668%   $240.5568   $240.56   $240.55   $240.60  
  Purchase #5 $69.94   7.841%   $75.424   $75.42   $75.40   $75.40  
  Purchase #6 $74.70   8.774%   $81.2542   $81.25   $81.25   $81.30  
  Purchase #7 $237.44   4.667%   $248.5213   $248.52   $248.50   $248.50  
  7 purchase totals = $1,152.25       $1,238.8150   $1,238.81   $1,238.75   $1,238.90