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 $191.81   10.271%   $211.5108   $211.51   $211.50   $211.50  
  Purchase #2 $183.74   6.162%   $195.0621   $195.06   $195.05   $195.10  
  Purchase #3 $30.74   11.575%   $34.2982   $34.30   $34.30   $34.30  
  Purchase #4 $110.57   6.649%   $117.9218   $117.92   $117.90   $117.90  
  Purchase #5 $154.25   4.356%   $160.9691   $160.97   $160.95   $161.00  
  Purchase #6 $229.87   12.656%   $258.9623   $258.96   $258.95   $259.00  
  Purchase #7 $28.52   12.868%   $32.19   $32.19   $32.20   $32.20  
  7 purchase totals = $929.50       $1,010.9143   $1,010.91   $1,010.85   $1,011.00