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 $248.30   6.652%   $264.8169   $264.82   $264.80   $264.80  
  Purchase #2 $122.90   5.417%   $129.5575   $129.56   $129.55   $129.60  
  Purchase #3 $78.32   11.788%   $87.5524   $87.55   $87.55   $87.60  
  Purchase #4 $232.87   3.521%   $241.0694   $241.07   $241.05   $241.10  
  Purchase #5 $187.26   12.385%   $210.4522   $210.45   $210.45   $210.50  
  Purchase #6 $44.52   6.347%   $47.3457   $47.35   $47.35   $47.30  
  Purchase #7 $214.82   3.861%   $223.1142   $223.11   $223.10   $223.10  
  7 purchase totals = $1,128.99       $1,203.9083   $1,203.91   $1,203.85   $1,204.00