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 $60.83   10.239%   $67.0584   $67.06   $67.05   $67.10  
  Purchase #2 $209.85   12.529%   $236.1421   $236.14   $236.15   $236.10  
  Purchase #3 $103.64   12.548%   $116.6447   $116.64   $116.65   $116.60  
  Purchase #4 $173.73   8.819%   $189.0512   $189.05   $189.05   $189.10  
  Purchase #5 $210.76   5.257%   $221.8397   $221.84   $221.85   $221.80  
  Purchase #6 $144.57   6.156%   $153.4697   $153.47   $153.45   $153.50  
  Purchase #7 $147.48   7.194%   $158.0897   $158.09   $158.10   $158.10  
  7 purchase totals = $1,050.86       $1,142.2955   $1,142.29   $1,142.30   $1,142.30