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 $233.53   3.288%   $241.2085   $241.21   $241.20   $241.20  
  Purchase #2 $86.35   7.704%   $93.0024   $93.00   $93.00   $93.00  
  Purchase #3 $144.59   12.848%   $163.1669   $163.17   $163.15   $163.20  
  Purchase #4 $187.58   9.568%   $205.5277   $205.53   $205.55   $205.50  
  Purchase #5 $161.93   12.119%   $181.5543   $181.55   $181.55   $181.60  
  Purchase #6 $195.64   6.659%   $208.6677   $208.67   $208.65   $208.70  
  Purchase #7 $121.31   9.454%   $132.7786   $132.78   $132.80   $132.80  
  7 purchase totals = $1,130.93       $1,225.9061   $1,225.91   $1,225.90   $1,226.00