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 $125.70   6.203%   $133.4972   $133.50   $133.50   $133.50  
  Purchase #2 $246.62   8.634%   $267.9132   $267.91   $267.90   $267.90  
  Purchase #3 $23.33   8.336%   $25.2748   $25.27   $25.25   $25.30  
  Purchase #4 $181.69   12.356%   $204.1396   $204.14   $204.15   $204.10  
  Purchase #5 $236.93   4.833%   $248.3808   $248.38   $248.40   $248.40  
  Purchase #6 $89.91   5.820%   $95.1428   $95.14   $95.15   $95.10  
  Purchase #7 $63.94   4.580%   $66.8685   $66.87   $66.85   $66.90  
  7 purchase totals = $968.12       $1,041.2169   $1,041.21   $1,041.20   $1,041.20