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 $69.68   5.656%   $73.6211   $73.62   $73.60   $73.60  
  Purchase #2 $27.35   8.773%   $29.7494   $29.75   $29.75   $29.70  
  Purchase #3 $210.34   5.282%   $221.4502   $221.45   $221.45   $221.50  
  Purchase #4 $24.86   7.699%   $26.774   $26.77   $26.75   $26.80  
  Purchase #5 $208.46   5.459%   $219.8398   $219.84   $219.85   $219.80  
  Purchase #6 $190.51   11.169%   $211.7881   $211.79   $211.80   $211.80  
  Purchase #7 $51.57   7.416%   $55.3944   $55.39   $55.40   $55.40  
  7 purchase totals = $782.77       $838.6170   $838.61   $838.60   $838.60