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 $171.94   5.456%   $181.321   $181.32   $181.30   $181.30  
  Purchase #2 $152.41   7.519%   $163.8697   $163.87   $163.85   $163.90  
  Purchase #3 $44.80   11.689%   $50.0367   $50.04   $50.05   $50.00  
  Purchase #4 $183.30   5.560%   $193.4915   $193.49   $193.50   $193.50  
  Purchase #5 $49.91   5.410%   $52.6101   $52.61   $52.60   $52.60  
  Purchase #6 $143.54   13.393%   $162.7643   $162.76   $162.75   $162.80  
  Purchase #7 $174.74   9.121%   $190.678   $190.68   $190.70   $190.70  
  7 purchase totals = $920.64       $994.7713   $994.77   $994.75   $994.80