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 $159.58   13.611%   $181.3004   $181.30   $181.30   $181.30  
  Purchase #2 $218.25   10.401%   $240.9502   $240.95   $240.95   $241.00  
  Purchase #3 $60.43   5.576%   $63.7996   $63.80   $63.80   $63.80  
  Purchase #4 $155.40   8.585%   $168.7411   $168.74   $168.75   $168.70  
  Purchase #5 $177.55   10.864%   $196.839   $196.84   $196.85   $196.80  
  Purchase #6 $183.82   9.135%   $200.612   $200.61   $200.60   $200.60  
  Purchase #7 $178.67   6.343%   $190.003   $190.00   $190.00   $190.00  
  7 purchase totals = $1,133.70       $1,242.2453   $1,242.24   $1,242.25   $1,242.20