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 $180.36   12.820%   $203.4822   $203.48   $203.50   $203.50  
  Purchase #2 $115.62   10.456%   $127.7092   $127.71   $127.70   $127.70  
  Purchase #3 $44.47   7.256%   $47.6967   $47.70   $47.70   $47.70  
  Purchase #4 $92.76   6.694%   $98.9694   $98.97   $98.95   $99.00  
  Purchase #5 $112.88   13.629%   $128.2644   $128.26   $128.25   $128.30  
  Purchase #6 $141.76   7.817%   $152.8414   $152.84   $152.85   $152.80  
  Purchase #7 $164.94   7.665%   $177.5827   $177.58   $177.60   $177.60  
  7 purchase totals = $852.79       $936.5460   $936.54   $936.55   $936.60