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 $59.51   11.722%   $66.4858   $66.49   $66.50   $66.50  
  Purchase #2 $247.57   8.718%   $269.1532   $269.15   $269.15   $269.20  
  Purchase #3 $203.79   8.492%   $221.0958   $221.10   $221.10   $221.10  
  Purchase #4 $23.70   12.866%   $26.7492   $26.75   $26.75   $26.70  
  Purchase #5 $197.63   11.463%   $220.2843   $220.28   $220.30   $220.30  
  Purchase #6 $123.82   3.626%   $128.3097   $128.31   $128.30   $128.30  
  Purchase #7 $57.73   8.438%   $62.6013   $62.60   $62.60   $62.60  
  7 purchase totals = $913.75       $994.6793   $994.68   $994.70   $994.70