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 $64.51   6.598%   $68.7664   $68.77   $68.75   $68.80  
  Purchase #2 $152.92   6.219%   $162.4301   $162.43   $162.45   $162.40  
  Purchase #3 $101.63   8.166%   $109.9291   $109.93   $109.95   $109.90  
  Purchase #4 $249.90   6.483%   $266.101   $266.10   $266.10   $266.10  
  Purchase #5 $206.42   13.641%   $234.5778   $234.58   $234.60   $234.60  
  Purchase #6 $69.57   12.627%   $78.3546   $78.35   $78.35   $78.40  
  Purchase #7 $250.34   6.225%   $265.9237   $265.92   $265.90   $265.90  
  7 purchase totals = $1,095.29       $1,186.0827   $1,186.08   $1,186.10   $1,186.10