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 $55.84   8.112%   $60.3697   $60.37   $60.35   $60.40  
  Purchase #2 $227.75   13.396%   $258.2594   $258.26   $258.25   $258.30  
  Purchase #3 $95.80   11.241%   $106.5689   $106.57   $106.55   $106.60  
  Purchase #4 $180.69   3.627%   $187.2436   $187.24   $187.25   $187.20  
  Purchase #5 $198.28   11.779%   $221.6354   $221.64   $221.65   $221.60  
  Purchase #6 $136.86   9.560%   $149.9438   $149.94   $149.95   $149.90  
  Purchase #7 $34.79   5.223%   $36.6071   $36.61   $36.60   $36.60  
  7 purchase totals = $930.01       $1,020.6279   $1,020.63   $1,020.60   $1,020.60