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 $24.44   8.831%   $26.5983   $26.60   $26.60   $26.60  
  Purchase #2 $246.64   4.638%   $258.0792   $258.08   $258.10   $258.10  
  Purchase #3 $193.38   7.197%   $207.2976   $207.30   $207.30   $207.30  
  Purchase #4 $241.46   5.257%   $254.1536   $254.15   $254.15   $254.20  
  Purchase #5 $211.99   7.770%   $228.4616   $228.46   $228.45   $228.50  
  Purchase #6 $204.56   8.725%   $222.4079   $222.41   $222.40   $222.40  
  Purchase #7 $171.97   3.677%   $178.2933   $178.29   $178.30   $178.30  
  7 purchase totals = $1,294.44       $1,375.2915   $1,375.29   $1,375.30   $1,375.40