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 $50.54   11.792%   $56.4997   $56.50   $56.50   $56.50  
  Purchase #2 $219.51   8.848%   $238.9322   $238.93   $238.95   $238.90  
  Purchase #3 $64.87   10.593%   $71.7417   $71.74   $71.75   $71.70  
  Purchase #4 $238.87   13.795%   $271.8221   $271.82   $271.80   $271.80  
  Purchase #5 $202.45   13.388%   $229.554   $229.55   $229.55   $229.60  
  Purchase #6 $237.85   5.618%   $251.2124   $251.21   $251.20   $251.20  
  Purchase #7 $60.60   11.874%   $67.7956   $67.80   $67.80   $67.80  
  7 purchase totals = $1,074.69       $1,187.5577   $1,187.55   $1,187.55   $1,187.50