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 $217.98   11.280%   $242.5681   $242.57   $242.55   $242.60  
  Purchase #2 $56.45   6.137%   $59.9143   $59.91   $59.90   $59.90  
  Purchase #3 $83.56   13.153%   $94.5506   $94.55   $94.55   $94.60  
  Purchase #4 $248.58   12.832%   $280.4778   $280.48   $280.50   $280.50  
  Purchase #5 $202.56   7.416%   $217.5818   $217.58   $217.60   $217.60  
  Purchase #6 $226.72   11.566%   $252.9424   $252.94   $252.95   $252.90  
  Purchase #7 $178.59   3.558%   $184.9442   $184.94   $184.95   $184.90  
  7 purchase totals = $1,214.44       $1,332.9792   $1,332.97   $1,333.00   $1,333.00