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 $66.52   7.310%   $71.3826   $71.38   $71.40   $71.40  
  Purchase #2 $63.91   9.366%   $69.8958   $69.90   $69.90   $69.90  
  Purchase #3 $5.87   7.412%   $6.3051   $6.31   $6.30   $6.30  
  Purchase #4 $134.95   7.789%   $145.4613   $145.46   $145.45   $145.50  
  Purchase #5 $87.58   7.351%   $94.018   $94.02   $94.00   $94.00  
  Purchase #6 $223.49   10.589%   $247.1554   $247.16   $247.15   $247.20  
  Purchase #7 $208.76   6.113%   $221.5215   $221.52   $221.50   $221.50  
  7 purchase totals = $791.08       $855.7397   $855.75   $855.70   $855.80