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 $136.79   10.861%   $151.6468   $151.65   $151.65   $151.60  
  Purchase #2 $123.35   11.568%   $137.6191   $137.62   $137.60   $137.60  
  Purchase #3 $197.64   3.186%   $203.9368   $203.94   $203.95   $203.90  
  Purchase #4 $135.64   5.701%   $143.3728   $143.37   $143.35   $143.40  
  Purchase #5 $214.74   11.687%   $239.8367   $239.84   $239.85   $239.80  
  Purchase #6 $68.86   4.353%   $71.8575   $71.86   $71.85   $71.90  
  Purchase #7 $84.79   3.172%   $87.4795   $87.48   $87.50   $87.50  
  7 purchase totals = $961.81       $1,035.7492   $1,035.76   $1,035.75   $1,035.70