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 $237.59   13.613%   $269.9331   $269.93   $269.95   $269.90  
  Purchase #2 $195.95   7.346%   $210.3445   $210.34   $210.35   $210.30  
  Purchase #3 $47.53   4.558%   $49.6964   $49.70   $49.70   $49.70  
  Purchase #4 $21.34   4.105%   $22.216   $22.22   $22.20   $22.20  
  Purchase #5 $114.79   3.808%   $119.1612   $119.16   $119.15   $119.20  
  Purchase #6 $138.64   3.765%   $143.8598   $143.86   $143.85   $143.90  
  Purchase #7 $185.88   9.323%   $203.2096   $203.21   $203.20   $203.20  
  7 purchase totals = $941.72       $1,018.4206   $1,018.42   $1,018.40   $1,018.40