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 $50.37   7.158%   $53.9755   $53.98   $54.00   $54.00  
  Purchase #2 $184.96   12.209%   $207.5418   $207.54   $207.55   $207.50  
  Purchase #3 $204.89   5.499%   $216.1569   $216.16   $216.15   $216.20  
  Purchase #4 $227.48   8.628%   $247.107   $247.11   $247.10   $247.10  
  Purchase #5 $57.60   4.127%   $59.9772   $59.98   $60.00   $60.00  
  Purchase #6 $135.69   6.296%   $144.233   $144.23   $144.25   $144.20  
  Purchase #7 $91.55   6.356%   $97.3689   $97.37   $97.35   $97.40  
  7 purchase totals = $952.54       $1,026.3603   $1,026.37   $1,026.40   $1,026.40