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 $55.57   6.623%   $59.2504   $59.25   $59.25   $59.30  
  Purchase #2 $25.84   13.329%   $29.2842   $29.28   $29.30   $29.30  
  Purchase #3 $163.26   4.544%   $170.6785   $170.68   $170.70   $170.70  
  Purchase #4 $81.32   4.518%   $84.994   $84.99   $85.00   $85.00  
  Purchase #5 $16.81   10.860%   $18.6356   $18.64   $18.65   $18.60  
  Purchase #6 $246.62   12.324%   $277.0134   $277.01   $277.00   $277.00  
  Purchase #7 $111.62   13.737%   $126.9532   $126.95   $126.95   $127.00  
  7 purchase totals = $701.04       $766.8093   $766.80   $766.85   $766.90