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 $245.49   12.393%   $275.9136   $275.91   $275.90   $275.90  
  Purchase #2 $173.40   11.115%   $192.6734   $192.67   $192.65   $192.70  
  Purchase #3 $160.87   4.320%   $167.8196   $167.82   $167.80   $167.80  
  Purchase #4 $248.48   4.458%   $259.5572   $259.56   $259.55   $259.60  
  Purchase #5 $115.94   11.642%   $129.4377   $129.44   $129.45   $129.40  
  Purchase #6 $181.61   8.652%   $197.3229   $197.32   $197.30   $197.30  
  Purchase #7 $152.47   13.832%   $173.5597   $173.56   $173.55   $173.60  
  7 purchase totals = $1,278.26       $1,396.2841   $1,396.28   $1,396.20   $1,396.30