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 $226.37   6.515%   $241.118   $241.12   $241.10   $241.10  
  Purchase #2 $141.62   8.737%   $153.9933   $153.99   $154.00   $154.00  
  Purchase #3 $117.41   4.203%   $122.3447   $122.34   $122.35   $122.30  
  Purchase #4 $176.33   7.271%   $189.151   $189.15   $189.15   $189.20  
  Purchase #5 $192.88   8.547%   $209.3655   $209.37   $209.35   $209.40  
  Purchase #6 $47.96   10.784%   $53.132   $53.13   $53.15   $53.10  
  Purchase #7 $62.60   6.373%   $66.5895   $66.59   $66.60   $66.60  
  7 purchase totals = $965.17       $1,035.6940   $1,035.69   $1,035.70   $1,035.70