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 $85.86   9.157%   $93.7222   $93.72   $93.70   $93.70  
  Purchase #2 $125.91   12.585%   $141.7558   $141.76   $141.75   $141.80  
  Purchase #3 $92.46   9.408%   $101.1586   $101.16   $101.15   $101.20  
  Purchase #4 $199.52   4.263%   $208.0255   $208.03   $208.05   $208.00  
  Purchase #5 $203.58   4.233%   $212.1975   $212.20   $212.20   $212.20  
  Purchase #6 $23.67   13.307%   $26.8198   $26.82   $26.80   $26.80  
  Purchase #7 $129.39   5.233%   $136.161   $136.16   $136.15   $136.20  
  7 purchase totals = $860.39       $919.8404   $919.85   $919.80   $919.90