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 $248.27   8.664%   $269.7801   $269.78   $269.80   $269.80  
  Purchase #2 $196.53   13.258%   $222.5859   $222.59   $222.60   $222.60  
  Purchase #3 $87.27   6.795%   $93.2   $93.20   $93.20   $93.20  
  Purchase #4 $210.31   5.540%   $221.9612   $221.96   $221.95   $222.00  
  Purchase #5 $131.43   7.119%   $140.7865   $140.79   $140.80   $140.80  
  Purchase #6 $160.30   6.153%   $170.1633   $170.16   $170.15   $170.20  
  Purchase #7 $203.52   7.202%   $218.1775   $218.18   $218.20   $218.20  
  7 purchase totals = $1,237.63       $1,336.6545   $1,336.66   $1,336.70   $1,336.80