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 $196.88   6.569%   $209.813   $209.81   $209.80   $209.80  
  Purchase #2 $48.59   8.865%   $52.8975   $52.90   $52.90   $52.90  
  Purchase #3 $240.60   10.271%   $265.312   $265.31   $265.30   $265.30  
  Purchase #4 $218.40   11.216%   $242.8957   $242.90   $242.90   $242.90  
  Purchase #5 $209.85   6.576%   $223.6497   $223.65   $223.65   $223.60  
  Purchase #6 $62.62   9.710%   $68.7004   $68.70   $68.70   $68.70  
  Purchase #7 $9.35   11.654%   $10.4396   $10.44   $10.45   $10.40  
  7 purchase totals = $986.29       $1,073.7079   $1,073.71   $1,073.70   $1,073.60