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 $190.65   13.326%   $216.056   $216.06   $216.05   $216.10  
  Purchase #2 $155.99   13.839%   $177.5775   $177.58   $177.60   $177.60  
  Purchase #3 $45.49   9.818%   $49.9562   $49.96   $49.95   $50.00  
  Purchase #4 $150.39   9.263%   $164.3206   $164.32   $164.30   $164.30  
  Purchase #5 $159.53   9.857%   $175.2549   $175.25   $175.25   $175.30  
  Purchase #6 $202.71   6.772%   $216.4375   $216.44   $216.45   $216.40  
  Purchase #7 $151.50   3.775%   $157.2191   $157.22   $157.20   $157.20  
  7 purchase totals = $1,056.26       $1,156.8218   $1,156.83   $1,156.80   $1,156.90