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 $53.61   11.202%   $59.6154   $59.62   $59.60   $59.60  
  Purchase #2 $85.69   13.639%   $97.3773   $97.38   $97.40   $97.40  
  Purchase #3 $147.79   11.237%   $164.3972   $164.40   $164.40   $164.40  
  Purchase #4 $106.89   9.239%   $116.7656   $116.77   $116.75   $116.80  
  Purchase #5 $232.79   11.153%   $258.7531   $258.75   $258.75   $258.80  
  Purchase #6 $234.87   12.467%   $264.1512   $264.15   $264.15   $264.20  
  Purchase #7 $34.84   13.755%   $39.6322   $39.63   $39.65   $39.60  
  7 purchase totals = $896.48       $1,000.6920   $1,000.70   $1,000.70   $1,000.80