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 $43.62   8.194%   $47.1942   $47.19   $47.20   $47.20  
  Purchase #2 $101.74   6.342%   $108.1924   $108.19   $108.20   $108.20  
  Purchase #3 $228.48   11.616%   $255.0202   $255.02   $255.00   $255.00  
  Purchase #4 $106.54   9.813%   $116.9948   $116.99   $117.00   $117.00  
  Purchase #5 $32.28   5.585%   $34.0828   $34.08   $34.10   $34.10  
  Purchase #6 $209.56   10.521%   $231.6078   $231.61   $231.60   $231.60  
  Purchase #7 $246.88   8.796%   $268.5956   $268.60   $268.60   $268.60  
  7 purchase totals = $969.10       $1,061.6878   $1,061.68   $1,061.70   $1,061.70