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 $40.67   5.264%   $42.8109   $42.81   $42.80   $42.80  
  Purchase #2 $211.64   5.748%   $223.8051   $223.81   $223.80   $223.80  
  Purchase #3 $47.65   12.226%   $53.4757   $53.48   $53.50   $53.50  
  Purchase #4 $239.67   3.168%   $247.2627   $247.26   $247.25   $247.30  
  Purchase #5 $101.81   5.703%   $107.6162   $107.62   $107.60   $107.60  
  Purchase #6 $216.25   10.281%   $238.4827   $238.48   $238.50   $238.50  
  Purchase #7 $57.46   7.418%   $61.7224   $61.72   $61.70   $61.70  
  7 purchase totals = $915.15       $975.1757   $975.18   $975.15   $975.20