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 $120.35   9.354%   $131.6075   $131.61   $131.60   $131.60  
  Purchase #2 $202.71   9.835%   $222.6465   $222.65   $222.65   $222.60  
  Purchase #3 $50.58   4.703%   $52.9588   $52.96   $52.95   $53.00  
  Purchase #4 $62.79   4.521%   $65.6287   $65.63   $65.65   $65.60  
  Purchase #5 $221.26   4.674%   $231.6017   $231.60   $231.60   $231.60  
  Purchase #6 $65.63   5.588%   $69.2974   $69.30   $69.30   $69.30  
  Purchase #7 $179.93   8.542%   $195.2996   $195.30   $195.30   $195.30  
  7 purchase totals = $903.25       $969.0402   $969.05   $969.05   $969.00