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 $118.64   4.744%   $124.2683   $124.27   $124.25   $124.30  
  Purchase #2 $198.81   5.607%   $209.9573   $209.96   $209.95   $210.00  
  Purchase #3 $199.42   3.128%   $205.6579   $205.66   $205.65   $205.70  
  Purchase #4 $174.97   12.735%   $197.2524   $197.25   $197.25   $197.30  
  Purchase #5 $183.61   12.240%   $206.0839   $206.08   $206.10   $206.10  
  Purchase #6 $192.97   8.107%   $208.6141   $208.61   $208.60   $208.60  
  Purchase #7 $99.27   11.602%   $110.7873   $110.79   $110.80   $110.80  
  7 purchase totals = $1,167.69       $1,262.6212   $1,262.62   $1,262.60   $1,262.80