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 $61.63   12.354%   $69.2438   $69.24   $69.25   $69.20  
  Purchase #2 $206.89   12.772%   $233.314   $233.31   $233.30   $233.30  
  Purchase #3 $164.53   7.819%   $177.3946   $177.39   $177.40   $177.40  
  Purchase #4 $131.96   11.431%   $147.0443   $147.04   $147.05   $147.00  
  Purchase #5 $32.33   7.113%   $34.6296   $34.63   $34.65   $34.60  
  Purchase #6 $143.52   8.668%   $155.9603   $155.96   $155.95   $156.00  
  Purchase #7 $246.37   13.159%   $278.7898   $278.79   $278.80   $278.80  
  7 purchase totals = $987.23       $1,096.3764   $1,096.36   $1,096.40   $1,096.30