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 $52.77   3.781%   $54.7652   $54.77   $54.75   $54.80  
  Purchase #2 $94.57   10.730%   $104.7174   $104.72   $104.70   $104.70  
  Purchase #3 $235.28   11.369%   $262.029   $262.03   $262.05   $262.00  
  Purchase #4 $60.71   8.279%   $65.7362   $65.74   $65.75   $65.70  
  Purchase #5 $151.70   13.613%   $172.3509   $172.35   $172.35   $172.40  
  Purchase #6 $114.80   4.589%   $120.0682   $120.07   $120.05   $120.10  
  Purchase #7 $193.88   9.639%   $212.5681   $212.57   $212.55   $212.60  
  7 purchase totals = $903.71       $992.2350   $992.25   $992.20   $992.30