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 $243.55   10.429%   $268.9498   $268.95   $268.95   $268.90  
  Purchase #2 $141.89   8.797%   $154.3721   $154.37   $154.35   $154.40  
  Purchase #3 $146.56   6.446%   $156.0073   $156.01   $156.00   $156.00  
  Purchase #4 $212.93   13.280%   $241.2071   $241.21   $241.20   $241.20  
  Purchase #5 $233.85   6.171%   $248.2809   $248.28   $248.30   $248.30  
  Purchase #6 $232.48   8.442%   $252.106   $252.11   $252.10   $252.10  
  Purchase #7 $219.53   3.140%   $226.4232   $226.42   $226.40   $226.40  
  7 purchase totals = $1,430.79       $1,547.3464   $1,547.35   $1,547.30   $1,547.30