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 $237.55   13.234%   $268.9874   $268.99   $269.00   $269.00  
  Purchase #2 $204.43   10.454%   $225.8011   $225.80   $225.80   $225.80  
  Purchase #3 $241.40   8.850%   $262.7639   $262.76   $262.75   $262.80  
  Purchase #4 $132.77   4.202%   $138.349   $138.35   $138.35   $138.30  
  Purchase #5 $135.43   10.493%   $149.6407   $149.64   $149.65   $149.60  
  Purchase #6 $191.35   4.798%   $200.531   $200.53   $200.55   $200.50  
  Purchase #7 $220.40   9.448%   $241.2234   $241.22   $241.20   $241.20  
  7 purchase totals = $1,363.33       $1,487.2965   $1,487.29   $1,487.30   $1,487.20