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 $48.77   13.576%   $55.391   $55.39   $55.40   $55.40  
  Purchase #2 $148.96   11.298%   $165.7895   $165.79   $165.80   $165.80  
  Purchase #3 $156.94   12.294%   $176.2342   $176.23   $176.25   $176.20  
  Purchase #4 $223.94   9.737%   $245.745   $245.75   $245.75   $245.70  
  Purchase #5 $248.66   5.344%   $261.9484   $261.95   $261.95   $261.90  
  Purchase #6 $194.93   12.700%   $219.6861   $219.69   $219.70   $219.70  
  Purchase #7 $52.94   12.350%   $59.4781   $59.48   $59.50   $59.50  
  7 purchase totals = $1,075.14       $1,184.2723   $1,184.28   $1,184.35   $1,184.20