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 $48.55   10.819%   $53.8026   $53.80   $53.80   $53.80  
  Purchase #2 $233.89   13.448%   $265.3435   $265.34   $265.35   $265.30  
  Purchase #3 $149.28   4.286%   $155.6781   $155.68   $155.70   $155.70  
  Purchase #4 $222.48   11.855%   $248.855   $248.86   $248.85   $248.90  
  Purchase #5 $135.50   13.136%   $153.2993   $153.30   $153.30   $153.30  
  Purchase #6 $110.53   12.705%   $124.5728   $124.57   $124.55   $124.60  
  Purchase #7 $11.62   12.415%   $13.0626   $13.06   $13.05   $13.10  
  7 purchase totals = $911.85       $1,014.6139   $1,014.61   $1,014.60   $1,014.70