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 $192.69   11.117%   $214.1113   $214.11   $214.10   $214.10  
  Purchase #2 $67.28   4.326%   $70.1905   $70.19   $70.20   $70.20  
  Purchase #3 $159.71   12.725%   $180.0331   $180.03   $180.05   $180.00  
  Purchase #4 $84.99   3.868%   $88.2774   $88.28   $88.30   $88.30  
  Purchase #5 $241.42   10.820%   $267.5416   $267.54   $267.55   $267.50  
  Purchase #6 $136.90   11.762%   $153.0022   $153.00   $153.00   $153.00  
  Purchase #7 $149.91   12.410%   $168.5138   $168.51   $168.50   $168.50  
  7 purchase totals = $1,032.90       $1,141.6699   $1,141.66   $1,141.70   $1,141.60