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 $57.65   12.765%   $65.009   $65.01   $65.00   $65.00  
  Purchase #2 $192.63   6.233%   $204.6366   $204.64   $204.65   $204.60  
  Purchase #3 $9.90   5.119%   $10.4068   $10.41   $10.40   $10.40  
  Purchase #4 $241.72   10.702%   $267.5889   $267.59   $267.60   $267.60  
  Purchase #5 $215.28   8.642%   $233.8845   $233.88   $233.90   $233.90  
  Purchase #6 $159.80   5.172%   $168.0649   $168.06   $168.05   $168.10  
  Purchase #7 $237.63   7.293%   $254.9604   $254.96   $254.95   $255.00  
  7 purchase totals = $1,114.61       $1,204.5511   $1,204.55   $1,204.55   $1,204.60