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 $87.83   6.496%   $93.5354   $93.54   $93.55   $93.50  
  Purchase #2 $6.39   6.782%   $6.8234   $6.82   $6.80   $6.80  
  Purchase #3 $120.94   5.205%   $127.2349   $127.23   $127.25   $127.20  
  Purchase #4 $226.96   10.688%   $251.2175   $251.22   $251.20   $251.20  
  Purchase #5 $197.66   12.560%   $222.4861   $222.49   $222.50   $222.50  
  Purchase #6 $220.59   12.717%   $248.6424   $248.64   $248.65   $248.60  
  Purchase #7 $106.88   12.290%   $120.0156   $120.02   $120.00   $120.00  
  7 purchase totals = $967.25       $1,069.9553   $1,069.96   $1,069.95   $1,069.80