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 $57.32   13.396%   $64.9986   $65.00   $65.00   $65.00  
  Purchase #2 $158.94   9.203%   $173.5672   $173.57   $173.55   $173.60  
  Purchase #3 $178.29   8.485%   $193.4179   $193.42   $193.40   $193.40  
  Purchase #4 $239.51   13.264%   $271.2786   $271.28   $271.30   $271.30  
  Purchase #5 $114.93   4.594%   $120.2099   $120.21   $120.20   $120.20  
  Purchase #6 $78.50   5.500%   $82.8175   $82.82   $82.80   $82.80  
  Purchase #7 $171.26   10.221%   $188.7645   $188.76   $188.75   $188.80  
  7 purchase totals = $998.75       $1,095.0542   $1,095.06   $1,095.00   $1,095.10