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 $223.48   13.773%   $254.2599   $254.26   $254.25   $254.30  
  Purchase #2 $152.99   10.496%   $169.0478   $169.05   $169.05   $169.00  
  Purchase #3 $87.46   3.761%   $90.7494   $90.75   $90.75   $90.70  
  Purchase #4 $124.56   7.847%   $134.3342   $134.33   $134.35   $134.30  
  Purchase #5 $204.98   3.510%   $212.1748   $212.17   $212.15   $212.20  
  Purchase #6 $165.27   6.257%   $175.6109   $175.61   $175.60   $175.60  
  Purchase #7 $69.61   9.701%   $76.3629   $76.36   $76.35   $76.40  
  7 purchase totals = $1,028.35       $1,112.5399   $1,112.53   $1,112.50   $1,112.50