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 $23.86   9.346%   $26.09   $26.09   $26.10   $26.10  
  Purchase #2 $6.46   11.160%   $7.1809   $7.18   $7.20   $7.20  
  Purchase #3 $202.30   8.424%   $219.3418   $219.34   $219.35   $219.30  
  Purchase #4 $169.27   4.625%   $177.0987   $177.10   $177.10   $177.10  
  Purchase #5 $237.48   3.846%   $246.6135   $246.61   $246.60   $246.60  
  Purchase #6 $248.28   13.852%   $282.6717   $282.67   $282.65   $282.70  
  Purchase #7 $44.99   10.616%   $49.7661   $49.77   $49.75   $49.80  
  7 purchase totals = $932.64       $1,008.7627   $1,008.76   $1,008.75   $1,008.80