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 $125.66   12.455%   $141.311   $141.31   $141.30   $141.30  
  Purchase #2 $54.88   12.863%   $61.9392   $61.94   $61.95   $61.90  
  Purchase #3 $176.77   8.596%   $191.9651   $191.97   $191.95   $192.00  
  Purchase #4 $67.82   9.656%   $74.3687   $74.37   $74.35   $74.40  
  Purchase #5 $37.43   13.447%   $42.4632   $42.46   $42.45   $42.50  
  Purchase #6 $249.30   6.284%   $264.966   $264.97   $264.95   $265.00  
  Purchase #7 $204.56   6.855%   $218.5826   $218.58   $218.60   $218.60  
  7 purchase totals = $916.42       $995.5958   $995.60   $995.55   $995.70