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 $181.58   8.818%   $197.5917   $197.59   $197.60   $197.60  
  Purchase #2 $131.94   11.165%   $146.6711   $146.67   $146.65   $146.70  
  Purchase #3 $162.83   8.604%   $176.8399   $176.84   $176.85   $176.80  
  Purchase #4 $25.48   7.386%   $27.362   $27.36   $27.35   $27.40  
  Purchase #5 $134.58   12.425%   $151.3016   $151.30   $151.30   $151.30  
  Purchase #6 $17.41   6.642%   $18.5664   $18.57   $18.55   $18.60  
  Purchase #7 $155.66   5.144%   $163.6672   $163.67   $163.65   $163.70  
  7 purchase totals = $809.48       $881.9999   $882.00   $881.95   $882.10