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 $245.87   5.574%   $259.5748   $259.57   $259.55   $259.60  
  Purchase #2 $33.86   3.339%   $34.9906   $34.99   $35.00   $35.00  
  Purchase #3 $140.59   5.846%   $148.8089   $148.81   $148.80   $148.80  
  Purchase #4 $176.52   11.116%   $196.142   $196.14   $196.15   $196.10  
  Purchase #5 $134.84   9.279%   $147.3518   $147.35   $147.35   $147.40  
  Purchase #6 $246.79   9.141%   $269.3491   $269.35   $269.35   $269.30  
  Purchase #7 $156.56   7.237%   $167.8902   $167.89   $167.90   $167.90  
  7 purchase totals = $1,135.03       $1,224.1074   $1,224.10   $1,224.10   $1,224.10