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 $178.66   13.831%   $203.3705   $203.37   $203.35   $203.40  
  Purchase #2 $137.49   3.814%   $142.7339   $142.73   $142.75   $142.70  
  Purchase #3 $165.72   5.633%   $175.055   $175.06   $175.05   $175.10  
  Purchase #4 $167.65   10.253%   $184.8392   $184.84   $184.85   $184.80  
  Purchase #5 $141.32   13.260%   $160.059   $160.06   $160.05   $160.10  
  Purchase #6 $248.44   7.106%   $266.0941   $266.09   $266.10   $266.10  
  Purchase #7 $68.52   6.760%   $73.152   $73.15   $73.15   $73.20  
  7 purchase totals = $1,107.80       $1,205.3037   $1,205.30   $1,205.30   $1,205.40