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 $243.94   9.486%   $267.0801   $267.08   $267.10   $267.10  
  Purchase #2 $27.63   6.574%   $29.4464   $29.45   $29.45   $29.40  
  Purchase #3 $71.52   10.293%   $78.8816   $78.88   $78.90   $78.90  
  Purchase #4 $119.50   9.456%   $130.7999   $130.80   $130.80   $130.80  
  Purchase #5 $98.79   9.256%   $107.934   $107.93   $107.95   $107.90  
  Purchase #6 $165.45   5.538%   $174.6126   $174.61   $174.60   $174.60  
  Purchase #7 $15.31   7.700%   $16.4889   $16.49   $16.50   $16.50  
  7 purchase totals = $742.14       $805.2435   $805.24   $805.30   $805.20