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 $249.35   6.242%   $264.9144   $264.91   $264.90   $264.90  
  Purchase #2 $20.49   3.583%   $21.2242   $21.22   $21.20   $21.20  
  Purchase #3 $205.41   10.370%   $226.711   $226.71   $226.70   $226.70  
  Purchase #4 $111.77   5.554%   $117.9777   $117.98   $118.00   $118.00  
  Purchase #5 $236.77   6.778%   $252.8183   $252.82   $252.80   $252.80  
  Purchase #6 $219.33   5.598%   $231.6081   $231.61   $231.60   $231.60  
  Purchase #7 $130.97   12.297%   $147.0754   $147.08   $147.10   $147.10  
  7 purchase totals = $1,174.09       $1,262.3291   $1,262.33   $1,262.30   $1,262.30