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 $216.49   11.571%   $241.5401   $241.54   $241.55   $241.50  
  Purchase #2 $195.93   11.260%   $217.9917   $217.99   $218.00   $218.00  
  Purchase #3 $84.37   6.286%   $89.6735   $89.67   $89.65   $89.70  
  Purchase #4 $150.72   7.446%   $161.9426   $161.94   $161.95   $161.90  
  Purchase #5 $237.47   3.489%   $245.7553   $245.76   $245.75   $245.80  
  Purchase #6 $134.71   4.293%   $140.4931   $140.49   $140.50   $140.50  
  Purchase #7 $135.60   5.873%   $143.5638   $143.56   $143.55   $143.60  
  7 purchase totals = $1,155.29       $1,240.9601   $1,240.95   $1,240.95   $1,241.00