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 $43.90   8.750%   $47.7413   $47.74   $47.75   $47.70  
  Purchase #2 $81.66   7.238%   $87.5706   $87.57   $87.55   $87.60  
  Purchase #3 $71.48   5.367%   $75.3163   $75.32   $75.30   $75.30  
  Purchase #4 $5.41   8.585%   $5.8744   $5.87   $5.85   $5.90  
  Purchase #5 $120.81   5.371%   $127.2987   $127.30   $127.30   $127.30  
  Purchase #6 $190.38   9.636%   $208.725   $208.73   $208.75   $208.70  
  Purchase #7 $48.78   11.385%   $54.3336   $54.33   $54.35   $54.30  
  7 purchase totals = $562.42       $606.8599   $606.86   $606.85   $606.80