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 $60.89   5.718%   $64.3717   $64.37   $64.35   $64.40  
  Purchase #2 $124.52   4.765%   $130.4534   $130.45   $130.45   $130.50  
  Purchase #3 $241.58   12.140%   $270.9078   $270.91   $270.90   $270.90  
  Purchase #4 $238.87   12.540%   $268.8243   $268.82   $268.80   $268.80  
  Purchase #5 $80.81   4.798%   $84.6873   $84.69   $84.70   $84.70  
  Purchase #6 $92.58   11.286%   $103.0286   $103.03   $103.05   $103.00  
  Purchase #7 $185.29   6.379%   $197.1096   $197.11   $197.10   $197.10  
  7 purchase totals = $1,024.54       $1,119.3827   $1,119.38   $1,119.35   $1,119.40