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 $237.61   11.454%   $264.8258   $264.83   $264.85   $264.80  
  Purchase #2 $160.84   9.263%   $175.7386   $175.74   $175.75   $175.70  
  Purchase #3 $243.70   10.675%   $269.715   $269.72   $269.70   $269.70  
  Purchase #4 $48.58   10.328%   $53.5973   $53.60   $53.60   $53.60  
  Purchase #5 $226.25   12.136%   $253.7077   $253.71   $253.70   $253.70  
  Purchase #6 $7.66   9.847%   $8.4143   $8.41   $8.40   $8.40  
  Purchase #7 $248.31   3.228%   $256.3254   $256.33   $256.35   $256.30  
  7 purchase totals = $1,172.95       $1,282.3241   $1,282.34   $1,282.35   $1,282.20