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 $232.30   9.210%   $253.6948   $253.69   $253.70   $253.70  
  Purchase #2 $84.94   12.329%   $95.4123   $95.41   $95.40   $95.40  
  Purchase #3 $44.52   8.369%   $48.2459   $48.25   $48.25   $48.20  
  Purchase #4 $96.62   6.550%   $102.9486   $102.95   $102.95   $102.90  
  Purchase #5 $62.78   13.820%   $71.4562   $71.46   $71.45   $71.50  
  Purchase #6 $103.30   10.721%   $114.3748   $114.37   $114.35   $114.40  
  Purchase #7 $64.74   9.794%   $71.0806   $71.08   $71.10   $71.10  
  7 purchase totals = $689.20       $757.2132   $757.21   $757.20   $757.20