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 $248.56   13.725%   $282.6749   $282.67   $282.65   $282.70  
  Purchase #2 $120.68   8.250%   $130.6361   $130.64   $130.65   $130.60  
  Purchase #3 $133.84   12.745%   $150.8979   $150.90   $150.90   $150.90  
  Purchase #4 $33.58   11.184%   $37.3356   $37.34   $37.35   $37.30  
  Purchase #5 $221.25   11.267%   $246.1782   $246.18   $246.20   $246.20  
  Purchase #6 $209.74   3.460%   $216.997   $217.00   $217.00   $217.00  
  Purchase #7 $186.50   3.590%   $193.1954   $193.20   $193.20   $193.20  
  7 purchase totals = $1,154.15       $1,257.9151   $1,257.93   $1,257.95   $1,257.90