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 $166.59   5.258%   $175.3493   $175.35   $175.35   $175.30  
  Purchase #2 $71.57   7.106%   $76.6558   $76.66   $76.65   $76.70  
  Purchase #3 $233.29   6.678%   $248.8691   $248.87   $248.85   $248.90  
  Purchase #4 $146.85   7.492%   $157.852   $157.85   $157.85   $157.90  
  Purchase #5 $90.58   7.313%   $97.2041   $97.20   $97.20   $97.20  
  Purchase #6 $68.72   12.856%   $77.5546   $77.55   $77.55   $77.60  
  Purchase #7 $209.26   6.726%   $223.3348   $223.33   $223.35   $223.30  
  7 purchase totals = $986.86       $1,056.8197   $1,056.81   $1,056.80   $1,056.90