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 $57.71   10.228%   $63.6126   $63.61   $63.60   $63.60  
  Purchase #2 $153.52   11.551%   $171.2531   $171.25   $171.25   $171.30  
  Purchase #3 $26.33   5.683%   $27.8263   $27.83   $27.85   $27.80  
  Purchase #4 $169.96   4.717%   $177.977   $177.98   $178.00   $178.00  
  Purchase #5 $224.58   7.422%   $241.2483   $241.25   $241.25   $241.20  
  Purchase #6 $50.99   7.206%   $54.6643   $54.66   $54.65   $54.70  
  Purchase #7 $235.74   12.693%   $265.6625   $265.66   $265.65   $265.70  
  7 purchase totals = $918.83       $1,002.2441   $1,002.24   $1,002.25   $1,002.30