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 $54.76   8.843%   $59.6024   $59.60   $59.60   $59.60  
  Purchase #2 $167.35   6.172%   $177.6788   $177.68   $177.70   $177.70  
  Purchase #3 $233.56   7.818%   $251.8197   $251.82   $251.80   $251.80  
  Purchase #4 $112.91   7.601%   $121.4923   $121.49   $121.50   $121.50  
  Purchase #5 $64.32   13.663%   $73.108   $73.11   $73.10   $73.10  
  Purchase #6 $227.95   13.594%   $258.9375   $258.94   $258.95   $258.90  
  Purchase #7 $152.42   12.417%   $171.346   $171.35   $171.35   $171.30  
  7 purchase totals = $1,013.27       $1,113.9847   $1,113.99   $1,114.00   $1,113.90