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 $24.99   4.380%   $26.0846   $26.08   $26.10   $26.10  
  Purchase #2 $176.84   12.187%   $198.3915   $198.39   $198.40   $198.40  
  Purchase #3 $226.65   13.717%   $257.7396   $257.74   $257.75   $257.70  
  Purchase #4 $197.40   5.554%   $208.3636   $208.36   $208.35   $208.40  
  Purchase #5 $59.89   9.717%   $65.7095   $65.71   $65.70   $65.70  
  Purchase #6 $102.86   5.140%   $108.147   $108.15   $108.15   $108.10  
  Purchase #7 $87.36   10.344%   $96.3965   $96.40   $96.40   $96.40  
  7 purchase totals = $875.99       $960.8323   $960.83   $960.85   $960.80