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 $112.80   12.416%   $126.8052   $126.81   $126.80   $126.80  
  Purchase #2 $142.28   11.370%   $158.4572   $158.46   $158.45   $158.50  
  Purchase #3 $76.95   12.193%   $86.3325   $86.33   $86.35   $86.30  
  Purchase #4 $65.52   6.744%   $69.9387   $69.94   $69.95   $69.90  
  Purchase #5 $169.29   5.412%   $178.452   $178.45   $178.45   $178.50  
  Purchase #6 $57.95   9.870%   $63.6697   $63.67   $63.65   $63.70  
  Purchase #7 $213.56   13.334%   $242.0361   $242.04   $242.05   $242.00  
  7 purchase totals = $838.35       $925.6914   $925.70   $925.70   $925.70