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 $61.45   11.717%   $68.6501   $68.65   $68.65   $68.70  
  Purchase #2 $241.90   6.451%   $257.505   $257.51   $257.50   $257.50  
  Purchase #3 $238.61   12.716%   $268.9516   $268.95   $268.95   $269.00  
  Purchase #4 $160.69   10.347%   $177.3166   $177.32   $177.30   $177.30  
  Purchase #5 $138.99   9.776%   $152.5777   $152.58   $152.60   $152.60  
  Purchase #6 $48.35   13.443%   $54.8497   $54.85   $54.85   $54.80  
  Purchase #7 $225.99   12.849%   $255.0275   $255.03   $255.05   $255.00  
  7 purchase totals = $1,115.98       $1,234.8782   $1,234.89   $1,234.90   $1,234.90